Hi everyone! As we're reaching the end of this year and as AI becomes smarter, I'd like to write such a blog, motivated by similar blogs [by](https://mirror.codeforces.com/blog/entry/108940) [user:adamant,2024-12-22], [by](https://mirror.codeforces.com/blog/entry/108595) [user:tibinyte,2024-12-22], [by](https://mirror.codeforces.com/blog/entry/113093) [user:antontrygubO_o,2024-12-22], [by](https://mirror.codeforces.com/blog/entry/113720) [user:wuhudsm,2024-12-22] and [by](https://mirror.codeforces.com/blog/entry/127391) [user:satyam343,2024-12-22].↵
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I am a member of the [SUA Programming Contest Problem Setter Team](https://sua.ac), so most of the problems I authored are for the onsite contests prepared by our team. I would like to thank all our team members for discussing the problems with me, and preparing some problems for me after I attended work. What's more, I would like to thank them for being kind and supportive friends in my everyday life. Without them, my world will become dim.↵
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It is astonishing to find out how many of these problems are related to my life. There are ideas from the (board) games I played, from the songs I listened to, and even from the places I've passed by. I can vividly remember how I came up with the idea, how I discuss it with my friends, how I learned new algorithms through preparing the problems when I wrote this blog. This is not just a collection of my problems, it even feels like a diary for my past years. I don't care about how smart AI might become, I just felt grateful that I had the chance to share my life with so many friends and contestants through these problems. Thank you, my dear competitive programming community, for giving me this unforgettable experience.↵
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This is not a comprehensive list as it only contains publicly available problems. I'll try to update this blog each time after we make our new contests public. Also the ratings below are a (maybe very biased) estimation from my perspective, so it might not be precise.↵
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| # | Problem | Contest | Rating (Est.) | Tags | Comments |↵
| --- | --- | --- | --- | --- | --- |↵
| 125 | [Bingo](https://mirror.codeforces.com/gym/105484/problem/I) | 2024 ICPC Nanjing | 2600 | combinatorics | Idea from a [meme](/predownloaded/d5/84/d5846a642a985896d13e2e78e552d3efa0407770.jpg). |↵
| 124 | [Binary Tree](https://mirror.codeforces.com/gym/105484/problem/G) | 2024 ICPC Nanjing | 2000 | interactive, trees, divide and conquer | |↵
| 123 | [Strips](https://mirror.codeforces.com/gym/105484/problem/K) | 2024 ICPC Nanjing | 1800 | constructive, greedy | |↵
| 122 | [Social Media](https://mirror.codeforces.com/gym/105484/problem/J) | 2024 ICPC Nanjing | 1400 | sortings, enumeration | |↵
| 121 | [Left Shifting 3](https://mirror.codeforces.com/gym/105484/problem/E) | 2024 ICPC Nanjing | 1200 | enumeration | |↵
| 120 | [Stop the Castle 2](https://mirror.codeforces.com/gym/105386/problem/C) |22024 ICPC Kunming Invitational | 2600 | bipartite matching | |↵
| 119 | [Collect the Coins](https://mirror.codeforces.com/gym/105386/problem/F) |22024 ICPC Kunming Invitational | 2400 | binary search, dp | One of the problems I liked, as the key observation is nice. |↵
| 118 | [Subarray](https://mirror.codeforces.com/gym/105386/problem/H) |22024 ICPC Kunming Invitational | 2500 | fft | |↵
| 117 | [Trails](https://mirror.codeforces.com/gym/105386/problem/L) |22024 ICPC Kunming Invitational | 2300 | binary search, dp | Idea from the board game *[Trails](https://boardgamegeek.com/boardgame/338628/trails)*, although it is not very related to the game mechanism. One of the problems I liked, as it requires the contestants to have a good understanding on using binary search to calculate LIS. |↵
| 116 | [The Quest for El Dorado](https://mirror.codeforces.com/gym/105386/problem/J) |22024 ICPC Kunming Invitational | 2200 | shortest paths, data structures | Idea from the board game *[The Quest for El Dorado](https://boardgamegeek.com/boardgame/217372/the-quest-for-el-dorado)*. |↵
| 115 | [Italian Cuisine](https://mirror.codeforces.com/gym/105386/problem/M) |22024 ICPC Kunming Invitational | 1900 | geometry | |↵
| 114 | [Relearn through Review](https://mirror.codeforces.com/gym/105386/problem/E) |22024 ICPC Kunming Invitational | 1900 | math theory | |↵
| 113 | [Two-star Contest](https://mirror.codeforces.com/gym/105386/problem/A) |22024 ICPC Kunming Invitational | 1600 | greedy, constructive | Idea came from the event that [some experts ranked ICPC as a two-star contest](https://www.ceracu.org.cn/nd.jsp?fromColId=2&id=236), because they can't get the statistics about ICPC so they just esimate them with the lower-bounds. |↵
| 112 | [Left Shifting 2](https://mirror.codeforces.com/gym/105386/problem/I) |22024 ICPC Kunming Invitational | 1400 | enumeration | |↵
| 111 | [Gold Medal](https://mirror.codeforces.com/gym/105386/problem/B) |22024 ICPC Kunming Invitational | 1200 | sortings | Idea came from the fact that there are 5 contests going on at the same time in that weekend. |↵
| 110 | [Triangle](https://mirror.codeforces.com/gym/105385/problem/B) | 2024 CCPC Shandong Invitational | 3000 | strings, combinatorics | |↵
| 109 | [Palindromic Polygon](https://mirror.codeforces.com/gym/105385/problem/M) | 2024 CCPC Shandong Invitational | 2300 | geometry, dp | |↵
| 108 | [Stop the Castle](https://mirror.codeforces.com/gym/105385/problem/H) | 2024 CCPC Shandong Invitational | 2200 | bipartite matching | |↵
| 107 | [Hero of the Kingdom](https://mirror.codeforces.com/gym/105385/problem/D) | 2024 CCPC Shandong Invitational | 2000 | sqrt trick | Idea from the game *[Hero of the Kingdom](https://store.steampowered.com/app/259550/)*. |↵
| 106 | [Colorful Segments 2](https://mirror.codeforces.com/gym/105385/problem/C) | 2024 CCPC Shandong Invitational | 1700 | sortings, combinatorics | |↵
| 105 | [Divide the Sequence](https://mirror.codeforces.com/gym/105385/problem/F) | 2024 CCPC Shandong Invitational | 1600 | suffix sums, greedy | Coincides with [CF1175D](https://mirror.codeforces.com/problemset/problem/1175/D). |↵
| 104 | [Printer](https://mirror.codeforces.com/gym/105385/problem/A) | 2024 CCPC Shandong Invitational | 1400 | binary search | |↵
| 103 | [Matrix](https://mirror.codeforces.com/gym/105385/problem/K) | 2024 CCPC Shandong Invitational | 1200 | constructive | |↵
| 102 | [Left Shifting](https://mirror.codeforces.com/gym/105385/problem/I) | 2024 CCPC Shandong Invitational | 800 | enumeration | |↵
| 101 | [Ticket to Ride](https://mirror.codeforces.com/gym/104901/problem/L) | 2023 ICPC Jinan | 2900 | dp | Idea from the board game *[Ticket to Ride](https://boardgamegeek.com/boardgame/9209/ticket-to-ride)*. One of the problems I liked, because the optimization needs some creative thinking. |↵
| 100 | [Rainbow Subarray](https://mirror.codeforces.com/gym/104901/problem/K) | 2023 ICPC Jinan | 1900 | two pointers, data structures | Idea from the board game *[TEN](https://boardgamegeek.com/boardgame/335609/ten)*. |↵
| 99 | [Largest Digit](https://mirror.codeforces.com/gym/104901/problem/D) | 2023 ICPC Jinan | 800 | enumeration | |↵
| 98 | [Red Black Tree](https://mirror.codeforces.com/gym/104821/problem/D) | 2023 ICPC Nanjing | 2600 | trees, dp, convex optimization | |↵
| 97 | [Trapping Rain Water](https://mirror.codeforces.com/gym/104821/problem/M) | 2023 ICPC Nanjing | 2200 | data structures | |↵
| 96 | [Elevator](https://mirror.codeforces.com/gym/104821/problem/L) | 2023 ICPC Nanjing | 1900 | greedy | |↵
| 95 | [Cool, It’s Yesterday Four Times More](https://mirror.codeforces.com/gym/104821/problem/A) | 2023 ICPC Nanjing | 1800 | bfs | |↵
| 94 | [Primitive Root](https://mirror.codeforces.com/gym/104821/problem/C) | 2023 ICPC Nanjing | 1600 | bitmasks | Idea from a <a href="/predownloaded/e0/99/e099cf4067ebc5e16c9364df9b6d0e4713de3ce8.png">meme</a>. |↵
| 93 | [Counter](https://mirror.codeforces.com/gym/104821/problem/I) | 2023 ICPC Nanjing | 1200 | sortings | |↵
| 92 | [Trie](https://mirror.codeforces.com/gym/104417/problem/C) | 2023 Shandong Provincial | 2600 | strings | One of the problems I liked, as it requires the contestants to have a good understanding on suffix arrays. |↵
| 91 | [Colorful Segments](https://mirror.codeforces.com/gym/104417/problem/F) | 2023 Shandong Provincial | 2400 | dp, data structures | |↵
| 90 | [Difficult Constructive Problem](https://mirror.codeforces.com/gym/104417/problem/K) | 2023 Shandong Provincial | 2200 | dp | One of the problems I liked. It looks like some constructive algorithms, but it is not. |↵
| 89 | [Building Company](https://mirror.codeforces.com/gym/104417/problem/B) | 2023 Shandong Provincial | 1700 | topological sort | Idea from the board game *[Splendor](https://boardgamegeek.com/boardgame/148228/splendor)*. |↵
| 88 | [Matching](https://mirror.codeforces.com/gym/104417/problem/G) | 2023 Shandong Provincial | 1200 | greedy | |↵
| 87 | [Orders](https://mirror.codeforces.com/gym/104417/problem/A) | 2023 Shandong Provincial | 1000 | sortings | |↵
| 86 | [Classic Problem](https://mirror.codeforces.com/gym/104369/problem/L) | 2023 Guangdong Provincial | 3000 | minimum spanning trees | Very standard Boruvka algorithm problems. |↵
| 85 | [Canvas](https://mirror.codeforces.com/gym/104369/problem/H) | 2023 Guangdong Provincial | 2600 | graphs, constructive | Idea from the board game *[Canvas](https://boardgamegeek.com/boardgame/290236/canvas)*. One of the problems I liked, as the modeling process is nice. |↵
| 84 | [Computational Geometry](https://mirror.codeforces.com/gym/104369/problem/M) | 2023 Guangdong Provincial | 2000 | geometry | |↵
| 83 | [New but Nostalgic Problem](https://mirror.codeforces.com/gym/104369/problem/E) | 2023 Guangdong Provincial | 1900 | strings, data structures, greedy | |↵
| 82 | [Base Station Construction](https://mirror.codeforces.com/gym/104369/problem/B) | 2023 Guangdong Provincial | 1900 | dp | |↵
| 81 | [Path Planning](https://mirror.codeforces.com/gym/104369/problem/I) | 2023 Guangdong Provincial | 1600 | binary search, sortings | |↵
| 80 | [Peg Solitaire](https://mirror.codeforces.com/gym/104369/problem/K) | 2023 Guangdong Provincial | 1400 | searching | Idea from the chess game *[Peg Solitaire](https://en.wikipedia.org/wiki/Peg_solitaire)*. |↵
| 79 | [Programming Contest](https://mirror.codeforces.com/gym/104369/problem/A) | 2023 Guangdong Provincial | 800 | enumeration | |↵
| 78 | [NaN in a Heap](https://mirror.codeforces.com/gym/104128/problem/K) | 2022 ICPC Nanjing | 2600 | combinatorics | I came up with the idea when dealing NaNs at my work. |↵
| 77 | [Drain the Water Tank](https://mirror.codeforces.com/gym/104128/problem/M) | 2022 ICPC Nanjing | 1900 | geometry | |↵
| 76 | [Ropeway](https://mirror.codeforces.com/gym/104128/problem/B) | 2022 ICPC Nanjing | 2100 | dp | |↵
| 75 | [Chat Program](https://mirror.codeforces.com/gym/104128/problem/D) | 2022 ICPC Nanjing | 1900 | enumeration, prefix sums | |↵
| 74 | [Stop, Yesterday Please No More](https://mirror.codeforces.com/gym/104128/problem/A) | 2022 ICPC Nanjing | 2000 | enumeration, prefix sums | |↵
| 73 | [Inscryption](https://mirror.codeforces.com/gym/104128/problem/G) | 2022 ICPC Nanjing | 1400 | greedy | Idea from the game *[Inscryption](https://store.steampowered.com/app/1092790/)*. |↵
| 72 | [Perfect Palindrome](https://mirror.codeforces.com/gym/104128/problem/I) | 2022 ICPC Nanjing | 1000 | greedy | |↵
| 71 | [Permutation on Tree](https://mirror.codeforces.com/gym/104373/problem/H) | 2021 ICPC Macau | 3000 | trees, dp | The complexity can be as low as $\mathcal{O}(n^2)$. |↵
| 70 | [Cyclic Buffer](https://mirror.codeforces.com/gym/104373/problem/G) | 2021 ICPC Macau | 2100 | dp, data structures | I came up with the idea when passing through a stereo garage. |↵
| 69 | [Laser Trap](https://mirror.codeforces.com/gym/104373/problem/C) | 2021 ICPC Macau | 1900 | geometry | |↵
| 68 | [Link-Cut Tree](https://mirror.codeforces.com/gym/104373/problem/K) | 2021 ICPC Macau | 1500 | greedy, dsu | |↵
| 67 | [Card Shark](https://qoj.ac/problem/4632) | 2022 Bytedance-Moscow Workshops Camp | 1900 | euler paths, greedy | Idea from the game *[Card Shark](https://store.steampowered.com/app/1371720/)*. |↵
| 66 | [Paimon's Tree](https://mirror.codeforces.com/gym/103470/problem/G) | 2021 ICPC Nanjing | 2700 | trees, dp | One of the problems I liked, as the idea is kind of different from the traditional dp on trees. |↵
| 65 | [Cloud Retainer's Game](https://mirror.codeforces.com/gym/103470/problem/I) | 2021 ICPC Nanjing | 2100 | DP | Idea from the mobile game *[World Flipper](https://world-flipper.fandom.com/wiki/World_Flipper_Wiki)*. |↵
| 64 | [Paimon Sorting](https://mirror.codeforces.com/gym/103470/problem/D) | 2021 ICPC Nanjing | 2100 | data structures | Idea from [Hacker News](http://news.ycombinator.com/item?id=28758106).↵
| 63 | [Direction Setting](https://mirror.codeforces.com/gym/103117/problem/F) | 2021 Sichuan Provincial | 2300 | flows | |↵
| 62 | [Nihongo wa Muzukashii Desu](https://mirror.codeforces.com/gym/103117/problem/H) | 2021 Sichuan Provincial | 800 | implementation | |↵
| 61 | [Chuanpai](https://mirror.codeforces.com/gym/103117/problem/A) | 2021 Sichuan Provincial | 800 | enumeration | |↵
| 60 | [Degree of Spanning Tree](https://mirror.codeforces.com/gym/102992/problem/D) | 2020 ICPC Nanjing | 2600 | greedy, constructive | |↵
| 59 | [Evil Coordinate](https://mirror.codeforces.com/gym/102992/problem/E) | 2020 ICPC Nanjing | 1700 | constructive | |↵
| 58 | [Let's Play Curling](https://mirror.codeforces.com/gym/102992/problem/L) | 2020 ICPC Nanjing | 1400 | greedy | I came up with the idea when watching a curling match on TV. |↵
| 57 | [Portal](https://pintia.cn/problem-sets/994805046380707840/exam/problems/type/7?problemSetProblemId=1336215880692482061&page=1) | 2020 GPLT | 2600 | data structures | |↵
| 56 | [Path to Infinity](https://pintia.cn/problem-sets/994805148990160896/exam/problems/type/7?problemSetProblemId=1478636592323768320) | 2019 Winter PAT Top Level | 2500 | meet in the middle | |↵
| 55 | [Coolbits](https://mirror.codeforces.com/gym/104460/problem/J) | 2019 Shaanxi Provincial | 1800 | bitmasks, greedy | |↵
| 54 | [0689](https://mirror.codeforces.com/gym/104460/problem/C) | 2019 Shaanxi Provincial | 1600 | enumeration | |↵
| 53 | [Grid with Arrows](https://mirror.codeforces.com/gym/104460/problem/B) | 2019 Shaanxi Provincial | 1400 | graphs | |↵
| 52 | [K-hour Clock](https://mirror.codeforces.com/gym/104460/problem/F) | 2019 Shaanxi Provincial | 1000 | number theory | |↵
| 51 | [Digit Product](https://mirror.codeforces.com/gym/104460/problem/L) | 2019 Shaanxi Provincial | 800 | implementation | |↵
| 50 | [Heap](https://mirror.codeforces.com/gym/104459/problem/G) | 2019 Shandong Provincial | 1900 | data structures | |↵
| 49 | [Triangle City](https://mirror.codeforces.com/gym/104459/problem/J) | 2019 Shandong Provincial | 1900 | shortest paths | |↵
| 48 | [Game on a Graph](https://mirror.codeforces.com/gym/104459/problem/F) | 2019 Shandong Provincial | 1000 | games, graphs | |↵
| 47 | [Stones in the Bucket](https://mirror.codeforces.com/gym/104459/problem/D) | 2019 Shandong Provincial | 1000 | greedy | |↵
| 46 | [Sekiro](https://mirror.codeforces.com/gym/104459/problem/A) | 2019 Shandong Provincial | 800 | implementation | |↵
| 45 | [Calandar](https://mirror.codeforces.com/gym/104459/problem/M) | 2019 Shandong Provincial | 800 | implementation | |↵
| 44 | [Array in the Pocket](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370497&page=31) | 2019 Zhejiang Provincial | 1900 | greedy, constructive | |↵
| 43 | [Strings in the Pocket](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370505&page=31) | 2019 Zhejiang Provincial | 2000 | palindromes | |↵
| 42 | [Element Swapping](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370496&page=31) | 2019 Zhejiang Provincial | 1700 | enumeration, math | |↵
| 41 | [Sequence in the Pocket](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370499&page=31) | 2019 Zhejiang Provincial | 1400 | sortings, enumeration | |↵
| 40 | [Fibonacci in the Pocket](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370503&page=31) | 2019 Zhejiang Provincial | 800 | math theory | |↵
| 39 | [Lucky 7 in the Pocket](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370501&page=31) | 2019 Zhejiang Provincial | 800 | enumeration | |↵
| 38 | [Strange Function](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370477&page=30) | 2019 ZJU School Contest | 2500 | data structures, enumeration | |↵
| 37 | [Robot Cleaner II](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370475&page=30) | 2019 ZJU School Contest | ? | genetic algorithm | Idea from the book *[Complexity: A Guided Tour](https://www.amazon.com/Complexity-Guided-Tour-Melanie-Mitchell/dp/0199798109)* Chapter 9. |↵
| 36 | [Robot Cleaner I](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370474&page=30) | 2019 ZJU School Contest | 1400 | bfs | Idea from the book *[Complexity: A Guided Tour](https://www.amazon.com/Complexity-Guided-Tour-Melanie-Mitchell/dp/0199798109)* Chapter 9. |↵
| 35 | [Postman](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370478&page=30) | 2019 ZJU School Contest | 1200 | greedy, sortings | |↵
| 34 | [Potion](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?page=30&problemSetProblemId=91827370476) | 2019 ZJU School Contest | 1000 | prefix sums | |↵
| 33 | [Kawa Exam](https://mirror.codeforces.com/gym/104270/problem/B) | 2018 ICPC Qingdao | 2500 | dsu on tree | A standard dsu on tree problem. I learned this algorithm for the first time when preparing for this problem. |↵
| 32 | [Airdrop](https://mirror.codeforces.com/gym/104270/problem/K) | 2018 ICPC Qingdao | 2000 | enumeration | |↵
| 31 | [Sub-cycle Graph](https://mirror.codeforces.com/gym/104270/problem/L) | 2018 ICPC Qingdao | 2300 | graphs, combinatorics | Almost all un-[official tutorials](https://sua.ac/wiki/2018-icpc-qingdao/l/) use generating function, which you actually don't need. |↵
| 30 | [Function and Function](https://mirror.codeforces.com/gym/104270/problem/M) | 2018 ICPC Qingdao | 1000 | implementation | |↵
| 29 | [Infinite Parenthesis Sequence](https://mirror.codeforces.com/gym/104566/problem/E) | 2018 ICPC Qingdao Online | 2800 | binary search, dp | The standard solution is a very tedious $\mathcal{O}(n)$ solution, which I already forgot. The current [tutorial](https://sua.ac/wiki/2018-icpc-qingdao-online/e/) uses jiangly's $\mathcal{O}(n\log n)$ method. |↵
| 28 | [Red Black Tree](https://mirror.codeforces.com/gym/104566/problem/B) | 2018 ICPC Qingdao Online | 2300 | trees, greedy, enumeration | |↵
| 27 | [Traveling on the Axis](https://mirror.codeforces.com/gym/104566/problem/H) | 2018 ICPC Qingdao Online | 1400 | enumeration, prefix sums | |↵
| 26 | [Halting Problem](https://mirror.codeforces.com/gym/104566/problem/C) | 2018 ICPC Qingdao Online | 1400 | bfs | |↵
| 25 | [Virtual Singers](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370288&page=30) | 2018 ZOJ June Monthly | 2800 | greedy | Idea from a [UTAU song](https://www.youtube.com/watch?v=t-tukFFpH4E). The standard solution uses some data structures, Claris has a better [greedy algorithm](https://www.cnblogs.com/clrs97/p/9901418.html) |↵
| 24 | [How Many Palindromes](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370289&page=30) | 2018 ZOJ June Monthly | 2200 | dp | |↵
| 23 | [Peer Review](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370282&page=30) | 2018 ZOJ June Monthly | 800 | greedy | |↵
| 22 | [Game on a Tree](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370265&page=30) | 2018 Zhejiang Provincial | 2500 | trees, dp | I came up with this idea when playing some interactive fiction game. However this problem coincides with [another problem](https://www.luogu.com.cn/problem/P7232), with a larger constraint. |↵
| 21 | [Sequence Swapping](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?page=30&problemSetProblemId=91827370261) | 2018 Zhejiang Provincial | 1600 | DP | |↵
| 20 | [Doki Doki Literature Club](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370269&page=30) | 2018 Zhejiang Provincial | 1100 | strings, sorting | Idea from the game *[Doki Doki Literature Club!](https://store.steampowered.com/app/698780/)*. |↵
| 19 | [Lucky 7](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370270&page=30) | 2018 Zhejiang Provincial | 800 | enumeration | |↵
| 18 | [Peak](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370258&page=30) | 2018 Zhejiang Provincial | 800 | implementation | |↵
| 17 | [Boolean Expression](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370242&page=30) | 2018 ZJU School Contest | 2200 | expression parsing, dp | Due to the 8M stack size limit during the contest, this problem becomes a bit harder. |↵
| 16 | [Traffic Light](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370241&page=30) | 2018 ZJU School Contest | 1300 | bfs | |↵
| 15 | [Mergeable Stack](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370237&page=30) | 2018 ZJU School Contest | 1300 | linked lists | |↵
| 14 | [PPAP](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?page=30&problemSetProblemId=91827370244) | 2018 ZJU School Contest | 800 | implementation | Idea from the pop song *[PPAP](https://www.youtube.com/watch?v=0E00Zuayv9Q)* and a <a href="/predownloaded/cb/01/cb0115e4187f291ae2cbf6f0d6d07b552f274475.png">meme complaining that the network in our university is bad</a>. |↵
| 13 | [Prime Set](https://qoj.ac/problem/9457) | 2017 CCPC Qinhuangdao | 2300 | bipartite matching | |↵
| 12 | [Balloon Robot](https://qoj.ac/problem/9450) | 2017 CCPC Qinhuangdao | 1700 | enumeration | |↵
| 11 | [String of CCPC](https://qoj.ac/problem/9454) | 2017 CCPC Qinhuangdao | 1200 | enumeration | |↵
| 10 | [One-Dimensional Maze](https://qoj.ac/problem/9461) | 2017 CCPC Qinhuangdao | 800 | enumeration | |↵
| 9 | [Card Game](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370094&page=29) | 2017 Zhejiang Provincial | 2600 | convex-hull trick | Super boring, super standard dynamic convex-hull trick problem. |↵
| 8 | [Binary Tree Restoring](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370092&page=29) | 2017 Zhejiang Provincial | 2100 | trees, dfs, constructive | |↵
| 7 | [Yet Another Game of Stones](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370091&page=29) | 2017 Zhejiang Provincial | 2200 | asymmetric games | |↵
| 6 | [Let's Chat](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370088&page=29) | 2017 Zhejiang Provincial | 1200 | implementation, sorting | |↵
| 5 | [Cooking Competition](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370085&page=29) | 2017 Zhejiang Provincial | 800 | implementation | Idea from the anime *[Miss Kobayashi's Dragon Maid](https://en.wikipedia.org/wiki/Miss_Kobayashi%27s_Dragon_Maid)*. |↵
| 4 | [Fibonacci Sequence Chicken Edition](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370066&page=29) | 2017 ZJU School Contest | 2200 | constructive | Calculate Fibonacci sequence with [Chicken](https://esolangs.org/wiki/Chicken) language. |↵
| 3 | [Edge to the Root](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370063&page=29) | 2017 ZJU School Contest | 2100 | trees, dfs | |↵
| 2 | [How Many Nines](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370064&page=29) | 2017 ZJU School Contest | 1200 | implementation, prefix sums | |↵
| 1 | [Marjar Cola](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?page=29&problemSetProblemId=91827370062) | 2017 ZJU School Contest | 1000 | implementation | My very first problem. |↵
↵
I am a member of the [SUA Programming Contest Problem Setter Team](https://sua.ac), so most of the problems I authored are for the onsite contests prepared by our team. I would like to thank all our team members for discussing the problems with me, and preparing some problems for me after I attended work. What's more, I would like to thank them for being kind and supportive friends in my everyday life. Without them, my world will become dim.↵
↵
It is astonishing to find out how many of these problems are related to my life. There are ideas from the (board) games I played, from the songs I listened to, and even from the places I've passed by. I can vividly remember how I came up with the idea, how I discuss it with my friends, how I learned new algorithms through preparing the problems when I wrote this blog. This is not just a collection of my problems, it even feels like a diary for my past years. I don't care about how smart AI might become, I just felt grateful that I had the chance to share my life with so many friends and contestants through these problems. Thank you, my dear competitive programming community, for giving me this unforgettable experience.↵
↵
This is not a comprehensive list as it only contains publicly available problems. I'll try to update this blog each time after we make our new contests public. Also the ratings below are a (maybe very biased) estimation from my perspective, so it might not be precise.↵
↵
| # | Problem | Contest | Rating (Est.) | Tags | Comments |↵
| --- | --- | --- | --- | --- | --- |↵
| 125 | [Bingo](https://mirror.codeforces.com/gym/105484/problem/I) | 2024 ICPC Nanjing | 2600 | combinatorics | Idea from a [meme](/predownloaded/d5/84/d5846a642a985896d13e2e78e552d3efa0407770.jpg). |↵
| 124 | [Binary Tree](https://mirror.codeforces.com/gym/105484/problem/G) | 2024 ICPC Nanjing | 2000 | interactive, trees, divide and conquer | |↵
| 123 | [Strips](https://mirror.codeforces.com/gym/105484/problem/K) | 2024 ICPC Nanjing | 1800 | constructive, greedy | |↵
| 122 | [Social Media](https://mirror.codeforces.com/gym/105484/problem/J) | 2024 ICPC Nanjing | 1400 | sortings, enumeration | |↵
| 121 | [Left Shifting 3](https://mirror.codeforces.com/gym/105484/problem/E) | 2024 ICPC Nanjing | 1200 | enumeration | |↵
| 120 | [Stop the Castle 2](https://mirror.codeforces.com/gym/105386/problem/C) |
| 119 | [Collect the Coins](https://mirror.codeforces.com/gym/105386/problem/F) |
| 118 | [Subarray](https://mirror.codeforces.com/gym/105386/problem/H) |
| 117 | [Trails](https://mirror.codeforces.com/gym/105386/problem/L) |
| 116 | [The Quest for El Dorado](https://mirror.codeforces.com/gym/105386/problem/J) |
| 115 | [Italian Cuisine](https://mirror.codeforces.com/gym/105386/problem/M) |
| 114 | [Relearn through Review](https://mirror.codeforces.com/gym/105386/problem/E) |
| 113 | [Two-star Contest](https://mirror.codeforces.com/gym/105386/problem/A) |
| 112 | [Left Shifting 2](https://mirror.codeforces.com/gym/105386/problem/I) |
| 111 | [Gold Medal](https://mirror.codeforces.com/gym/105386/problem/B) |
| 110 | [Triangle](https://mirror.codeforces.com/gym/105385/problem/B) | 2024 CCPC Shandong Invitational | 3000 | strings, combinatorics | |↵
| 109 | [Palindromic Polygon](https://mirror.codeforces.com/gym/105385/problem/M) | 2024 CCPC Shandong Invitational | 2300 | geometry, dp | |↵
| 108 | [Stop the Castle](https://mirror.codeforces.com/gym/105385/problem/H) | 2024 CCPC Shandong Invitational | 2200 | bipartite matching | |↵
| 107 | [Hero of the Kingdom](https://mirror.codeforces.com/gym/105385/problem/D) | 2024 CCPC Shandong Invitational | 2000 | sqrt trick | Idea from the game *[Hero of the Kingdom](https://store.steampowered.com/app/259550/)*. |↵
| 106 | [Colorful Segments 2](https://mirror.codeforces.com/gym/105385/problem/C) | 2024 CCPC Shandong Invitational | 1700 | sortings, combinatorics | |↵
| 105 | [Divide the Sequence](https://mirror.codeforces.com/gym/105385/problem/F) | 2024 CCPC Shandong Invitational | 1600 | suffix sums, greedy | Coincides with [CF1175D](https://mirror.codeforces.com/problemset/problem/1175/D). |↵
| 104 | [Printer](https://mirror.codeforces.com/gym/105385/problem/A) | 2024 CCPC Shandong Invitational | 1400 | binary search | |↵
| 103 | [Matrix](https://mirror.codeforces.com/gym/105385/problem/K) | 2024 CCPC Shandong Invitational | 1200 | constructive | |↵
| 102 | [Left Shifting](https://mirror.codeforces.com/gym/105385/problem/I) | 2024 CCPC Shandong Invitational | 800 | enumeration | |↵
| 101 | [Ticket to Ride](https://mirror.codeforces.com/gym/104901/problem/L) | 2023 ICPC Jinan | 2900 | dp | Idea from the board game *[Ticket to Ride](https://boardgamegeek.com/boardgame/9209/ticket-to-ride)*. One of the problems I liked, because the optimization needs some creative thinking. |↵
| 100 | [Rainbow Subarray](https://mirror.codeforces.com/gym/104901/problem/K) | 2023 ICPC Jinan | 1900 | two pointers, data structures | Idea from the board game *[TEN](https://boardgamegeek.com/boardgame/335609/ten)*. |↵
| 99 | [Largest Digit](https://mirror.codeforces.com/gym/104901/problem/D) | 2023 ICPC Jinan | 800 | enumeration | |↵
| 98 | [Red Black Tree](https://mirror.codeforces.com/gym/104821/problem/D) | 2023 ICPC Nanjing | 2600 | trees, dp, convex optimization | |↵
| 97 | [Trapping Rain Water](https://mirror.codeforces.com/gym/104821/problem/M) | 2023 ICPC Nanjing | 2200 | data structures | |↵
| 96 | [Elevator](https://mirror.codeforces.com/gym/104821/problem/L) | 2023 ICPC Nanjing | 1900 | greedy | |↵
| 95 | [Cool, It’s Yesterday Four Times More](https://mirror.codeforces.com/gym/104821/problem/A) | 2023 ICPC Nanjing | 1800 | bfs | |↵
| 94 | [Primitive Root](https://mirror.codeforces.com/gym/104821/problem/C) | 2023 ICPC Nanjing | 1600 | bitmasks | Idea from a <a href="/predownloaded/e0/99/e099cf4067ebc5e16c9364df9b6d0e4713de3ce8.png">meme</a>. |↵
| 93 | [Counter](https://mirror.codeforces.com/gym/104821/problem/I) | 2023 ICPC Nanjing | 1200 | sortings | |↵
| 92 | [Trie](https://mirror.codeforces.com/gym/104417/problem/C) | 2023 Shandong Provincial | 2600 | strings | One of the problems I liked, as it requires the contestants to have a good understanding on suffix arrays. |↵
| 91 | [Colorful Segments](https://mirror.codeforces.com/gym/104417/problem/F) | 2023 Shandong Provincial | 2400 | dp, data structures | |↵
| 90 | [Difficult Constructive Problem](https://mirror.codeforces.com/gym/104417/problem/K) | 2023 Shandong Provincial | 2200 | dp | One of the problems I liked. It looks like some constructive algorithms, but it is not. |↵
| 89 | [Building Company](https://mirror.codeforces.com/gym/104417/problem/B) | 2023 Shandong Provincial | 1700 | topological sort | Idea from the board game *[Splendor](https://boardgamegeek.com/boardgame/148228/splendor)*. |↵
| 88 | [Matching](https://mirror.codeforces.com/gym/104417/problem/G) | 2023 Shandong Provincial | 1200 | greedy | |↵
| 87 | [Orders](https://mirror.codeforces.com/gym/104417/problem/A) | 2023 Shandong Provincial | 1000 | sortings | |↵
| 86 | [Classic Problem](https://mirror.codeforces.com/gym/104369/problem/L) | 2023 Guangdong Provincial | 3000 | minimum spanning trees | Very standard Boruvka algorithm problems. |↵
| 85 | [Canvas](https://mirror.codeforces.com/gym/104369/problem/H) | 2023 Guangdong Provincial | 2600 | graphs, constructive | Idea from the board game *[Canvas](https://boardgamegeek.com/boardgame/290236/canvas)*. One of the problems I liked, as the modeling process is nice. |↵
| 84 | [Computational Geometry](https://mirror.codeforces.com/gym/104369/problem/M) | 2023 Guangdong Provincial | 2000 | geometry | |↵
| 83 | [New but Nostalgic Problem](https://mirror.codeforces.com/gym/104369/problem/E) | 2023 Guangdong Provincial | 1900 | strings, data structures, greedy | |↵
| 82 | [Base Station Construction](https://mirror.codeforces.com/gym/104369/problem/B) | 2023 Guangdong Provincial | 1900 | dp | |↵
| 81 | [Path Planning](https://mirror.codeforces.com/gym/104369/problem/I) | 2023 Guangdong Provincial | 1600 | binary search, sortings | |↵
| 80 | [Peg Solitaire](https://mirror.codeforces.com/gym/104369/problem/K) | 2023 Guangdong Provincial | 1400 | searching | Idea from the chess game *[Peg Solitaire](https://en.wikipedia.org/wiki/Peg_solitaire)*. |↵
| 79 | [Programming Contest](https://mirror.codeforces.com/gym/104369/problem/A) | 2023 Guangdong Provincial | 800 | enumeration | |↵
| 78 | [NaN in a Heap](https://mirror.codeforces.com/gym/104128/problem/K) | 2022 ICPC Nanjing | 2600 | combinatorics | I came up with the idea when dealing NaNs at my work. |↵
| 77 | [Drain the Water Tank](https://mirror.codeforces.com/gym/104128/problem/M) | 2022 ICPC Nanjing | 1900 | geometry | |↵
| 76 | [Ropeway](https://mirror.codeforces.com/gym/104128/problem/B) | 2022 ICPC Nanjing | 2100 | dp | |↵
| 75 | [Chat Program](https://mirror.codeforces.com/gym/104128/problem/D) | 2022 ICPC Nanjing | 1900 | enumeration, prefix sums | |↵
| 74 | [Stop, Yesterday Please No More](https://mirror.codeforces.com/gym/104128/problem/A) | 2022 ICPC Nanjing | 2000 | enumeration, prefix sums | |↵
| 73 | [Inscryption](https://mirror.codeforces.com/gym/104128/problem/G) | 2022 ICPC Nanjing | 1400 | greedy | Idea from the game *[Inscryption](https://store.steampowered.com/app/1092790/)*. |↵
| 72 | [Perfect Palindrome](https://mirror.codeforces.com/gym/104128/problem/I) | 2022 ICPC Nanjing | 1000 | greedy | |↵
| 71 | [Permutation on Tree](https://mirror.codeforces.com/gym/104373/problem/H) | 2021 ICPC Macau | 3000 | trees, dp | The complexity can be as low as $\mathcal{O}(n^2)$. |↵
| 70 | [Cyclic Buffer](https://mirror.codeforces.com/gym/104373/problem/G) | 2021 ICPC Macau | 2100 | dp, data structures | I came up with the idea when passing through a stereo garage. |↵
| 69 | [Laser Trap](https://mirror.codeforces.com/gym/104373/problem/C) | 2021 ICPC Macau | 1900 | geometry | |↵
| 68 | [Link-Cut Tree](https://mirror.codeforces.com/gym/104373/problem/K) | 2021 ICPC Macau | 1500 | greedy, dsu | |↵
| 67 | [Card Shark](https://qoj.ac/problem/4632) | 2022 Bytedance-Moscow Workshops Camp | 1900 | euler paths, greedy | Idea from the game *[Card Shark](https://store.steampowered.com/app/1371720/)*. |↵
| 66 | [Paimon's Tree](https://mirror.codeforces.com/gym/103470/problem/G) | 2021 ICPC Nanjing | 2700 | trees, dp | One of the problems I liked, as the idea is kind of different from the traditional dp on trees. |↵
| 65 | [Cloud Retainer's Game](https://mirror.codeforces.com/gym/103470/problem/I) | 2021 ICPC Nanjing | 2100 | DP | Idea from the mobile game *[World Flipper](https://world-flipper.fandom.com/wiki/World_Flipper_Wiki)*. |↵
| 64 | [Paimon Sorting](https://mirror.codeforces.com/gym/103470/problem/D) | 2021 ICPC Nanjing | 2100 | data structures | Idea from [Hacker News](http://news.ycombinator.com/item?id=28758106).↵
| 63 | [Direction Setting](https://mirror.codeforces.com/gym/103117/problem/F) | 2021 Sichuan Provincial | 2300 | flows | |↵
| 62 | [Nihongo wa Muzukashii Desu](https://mirror.codeforces.com/gym/103117/problem/H) | 2021 Sichuan Provincial | 800 | implementation | |↵
| 61 | [Chuanpai](https://mirror.codeforces.com/gym/103117/problem/A) | 2021 Sichuan Provincial | 800 | enumeration | |↵
| 60 | [Degree of Spanning Tree](https://mirror.codeforces.com/gym/102992/problem/D) | 2020 ICPC Nanjing | 2600 | greedy, constructive | |↵
| 59 | [Evil Coordinate](https://mirror.codeforces.com/gym/102992/problem/E) | 2020 ICPC Nanjing | 1700 | constructive | |↵
| 58 | [Let's Play Curling](https://mirror.codeforces.com/gym/102992/problem/L) | 2020 ICPC Nanjing | 1400 | greedy | I came up with the idea when watching a curling match on TV. |↵
| 57 | [Portal](https://pintia.cn/problem-sets/994805046380707840/exam/problems/type/7?problemSetProblemId=1336215880692482061&page=1) | 2020 GPLT | 2600 | data structures | |↵
| 56 | [Path to Infinity](https://pintia.cn/problem-sets/994805148990160896/exam/problems/type/7?problemSetProblemId=1478636592323768320) | 2019 Winter PAT Top Level | 2500 | meet in the middle | |↵
| 55 | [Coolbits](https://mirror.codeforces.com/gym/104460/problem/J) | 2019 Shaanxi Provincial | 1800 | bitmasks, greedy | |↵
| 54 | [0689](https://mirror.codeforces.com/gym/104460/problem/C) | 2019 Shaanxi Provincial | 1600 | enumeration | |↵
| 53 | [Grid with Arrows](https://mirror.codeforces.com/gym/104460/problem/B) | 2019 Shaanxi Provincial | 1400 | graphs | |↵
| 52 | [K-hour Clock](https://mirror.codeforces.com/gym/104460/problem/F) | 2019 Shaanxi Provincial | 1000 | number theory | |↵
| 51 | [Digit Product](https://mirror.codeforces.com/gym/104460/problem/L) | 2019 Shaanxi Provincial | 800 | implementation | |↵
| 50 | [Heap](https://mirror.codeforces.com/gym/104459/problem/G) | 2019 Shandong Provincial | 1900 | data structures | |↵
| 49 | [Triangle City](https://mirror.codeforces.com/gym/104459/problem/J) | 2019 Shandong Provincial | 1900 | shortest paths | |↵
| 48 | [Game on a Graph](https://mirror.codeforces.com/gym/104459/problem/F) | 2019 Shandong Provincial | 1000 | games, graphs | |↵
| 47 | [Stones in the Bucket](https://mirror.codeforces.com/gym/104459/problem/D) | 2019 Shandong Provincial | 1000 | greedy | |↵
| 46 | [Sekiro](https://mirror.codeforces.com/gym/104459/problem/A) | 2019 Shandong Provincial | 800 | implementation | |↵
| 45 | [Calandar](https://mirror.codeforces.com/gym/104459/problem/M) | 2019 Shandong Provincial | 800 | implementation | |↵
| 44 | [Array in the Pocket](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370497&page=31) | 2019 Zhejiang Provincial | 1900 | greedy, constructive | |↵
| 43 | [Strings in the Pocket](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370505&page=31) | 2019 Zhejiang Provincial | 2000 | palindromes | |↵
| 42 | [Element Swapping](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370496&page=31) | 2019 Zhejiang Provincial | 1700 | enumeration, math | |↵
| 41 | [Sequence in the Pocket](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370499&page=31) | 2019 Zhejiang Provincial | 1400 | sortings, enumeration | |↵
| 40 | [Fibonacci in the Pocket](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370503&page=31) | 2019 Zhejiang Provincial | 800 | math theory | |↵
| 39 | [Lucky 7 in the Pocket](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370501&page=31) | 2019 Zhejiang Provincial | 800 | enumeration | |↵
| 38 | [Strange Function](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370477&page=30) | 2019 ZJU School Contest | 2500 | data structures, enumeration | |↵
| 37 | [Robot Cleaner II](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370475&page=30) | 2019 ZJU School Contest | ? | genetic algorithm | Idea from the book *[Complexity: A Guided Tour](https://www.amazon.com/Complexity-Guided-Tour-Melanie-Mitchell/dp/0199798109)* Chapter 9. |↵
| 36 | [Robot Cleaner I](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370474&page=30) | 2019 ZJU School Contest | 1400 | bfs | Idea from the book *[Complexity: A Guided Tour](https://www.amazon.com/Complexity-Guided-Tour-Melanie-Mitchell/dp/0199798109)* Chapter 9. |↵
| 35 | [Postman](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370478&page=30) | 2019 ZJU School Contest | 1200 | greedy, sortings | |↵
| 34 | [Potion](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?page=30&problemSetProblemId=91827370476) | 2019 ZJU School Contest | 1000 | prefix sums | |↵
| 33 | [Kawa Exam](https://mirror.codeforces.com/gym/104270/problem/B) | 2018 ICPC Qingdao | 2500 | dsu on tree | A standard dsu on tree problem. I learned this algorithm for the first time when preparing for this problem. |↵
| 32 | [Airdrop](https://mirror.codeforces.com/gym/104270/problem/K) | 2018 ICPC Qingdao | 2000 | enumeration | |↵
| 31 | [Sub-cycle Graph](https://mirror.codeforces.com/gym/104270/problem/L) | 2018 ICPC Qingdao | 2300 | graphs, combinatorics | Almost all un-[official tutorials](https://sua.ac/wiki/2018-icpc-qingdao/l/) use generating function, which you actually don't need. |↵
| 30 | [Function and Function](https://mirror.codeforces.com/gym/104270/problem/M) | 2018 ICPC Qingdao | 1000 | implementation | |↵
| 29 | [Infinite Parenthesis Sequence](https://mirror.codeforces.com/gym/104566/problem/E) | 2018 ICPC Qingdao Online | 2800 | binary search, dp | The standard solution is a very tedious $\mathcal{O}(n)$ solution, which I already forgot. The current [tutorial](https://sua.ac/wiki/2018-icpc-qingdao-online/e/) uses jiangly's $\mathcal{O}(n\log n)$ method. |↵
| 28 | [Red Black Tree](https://mirror.codeforces.com/gym/104566/problem/B) | 2018 ICPC Qingdao Online | 2300 | trees, greedy, enumeration | |↵
| 27 | [Traveling on the Axis](https://mirror.codeforces.com/gym/104566/problem/H) | 2018 ICPC Qingdao Online | 1400 | enumeration, prefix sums | |↵
| 26 | [Halting Problem](https://mirror.codeforces.com/gym/104566/problem/C) | 2018 ICPC Qingdao Online | 1400 | bfs | |↵
| 25 | [Virtual Singers](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370288&page=30) | 2018 ZOJ June Monthly | 2800 | greedy | Idea from a [UTAU song](https://www.youtube.com/watch?v=t-tukFFpH4E). The standard solution uses some data structures, Claris has a better [greedy algorithm](https://www.cnblogs.com/clrs97/p/9901418.html) |↵
| 24 | [How Many Palindromes](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370289&page=30) | 2018 ZOJ June Monthly | 2200 | dp | |↵
| 23 | [Peer Review](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370282&page=30) | 2018 ZOJ June Monthly | 800 | greedy | |↵
| 22 | [Game on a Tree](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370265&page=30) | 2018 Zhejiang Provincial | 2500 | trees, dp | I came up with this idea when playing some interactive fiction game. However this problem coincides with [another problem](https://www.luogu.com.cn/problem/P7232), with a larger constraint. |↵
| 21 | [Sequence Swapping](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?page=30&problemSetProblemId=91827370261) | 2018 Zhejiang Provincial | 1600 | DP | |↵
| 20 | [Doki Doki Literature Club](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370269&page=30) | 2018 Zhejiang Provincial | 1100 | strings, sorting | Idea from the game *[Doki Doki Literature Club!](https://store.steampowered.com/app/698780/)*. |↵
| 19 | [Lucky 7](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370270&page=30) | 2018 Zhejiang Provincial | 800 | enumeration | |↵
| 18 | [Peak](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370258&page=30) | 2018 Zhejiang Provincial | 800 | implementation | |↵
| 17 | [Boolean Expression](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370242&page=30) | 2018 ZJU School Contest | 2200 | expression parsing, dp | Due to the 8M stack size limit during the contest, this problem becomes a bit harder. |↵
| 16 | [Traffic Light](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370241&page=30) | 2018 ZJU School Contest | 1300 | bfs | |↵
| 15 | [Mergeable Stack](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370237&page=30) | 2018 ZJU School Contest | 1300 | linked lists | |↵
| 14 | [PPAP](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?page=30&problemSetProblemId=91827370244) | 2018 ZJU School Contest | 800 | implementation | Idea from the pop song *[PPAP](https://www.youtube.com/watch?v=0E00Zuayv9Q)* and a <a href="/predownloaded/cb/01/cb0115e4187f291ae2cbf6f0d6d07b552f274475.png">meme complaining that the network in our university is bad</a>. |↵
| 13 | [Prime Set](https://qoj.ac/problem/9457) | 2017 CCPC Qinhuangdao | 2300 | bipartite matching | |↵
| 12 | [Balloon Robot](https://qoj.ac/problem/9450) | 2017 CCPC Qinhuangdao | 1700 | enumeration | |↵
| 11 | [String of CCPC](https://qoj.ac/problem/9454) | 2017 CCPC Qinhuangdao | 1200 | enumeration | |↵
| 10 | [One-Dimensional Maze](https://qoj.ac/problem/9461) | 2017 CCPC Qinhuangdao | 800 | enumeration | |↵
| 9 | [Card Game](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370094&page=29) | 2017 Zhejiang Provincial | 2600 | convex-hull trick | Super boring, super standard dynamic convex-hull trick problem. |↵
| 8 | [Binary Tree Restoring](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370092&page=29) | 2017 Zhejiang Provincial | 2100 | trees, dfs, constructive | |↵
| 7 | [Yet Another Game of Stones](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370091&page=29) | 2017 Zhejiang Provincial | 2200 | asymmetric games | |↵
| 6 | [Let's Chat](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370088&page=29) | 2017 Zhejiang Provincial | 1200 | implementation, sorting | |↵
| 5 | [Cooking Competition](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370085&page=29) | 2017 Zhejiang Provincial | 800 | implementation | Idea from the anime *[Miss Kobayashi's Dragon Maid](https://en.wikipedia.org/wiki/Miss_Kobayashi%27s_Dragon_Maid)*. |↵
| 4 | [Fibonacci Sequence Chicken Edition](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370066&page=29) | 2017 ZJU School Contest | 2200 | constructive | Calculate Fibonacci sequence with [Chicken](https://esolangs.org/wiki/Chicken) language. |↵
| 3 | [Edge to the Root](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370063&page=29) | 2017 ZJU School Contest | 2100 | trees, dfs | |↵
| 2 | [How Many Nines](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?problemSetProblemId=91827370064&page=29) | 2017 ZJU School Contest | 1200 | implementation, prefix sums | |↵
| 1 | [Marjar Cola](https://pintia.cn/problem-sets/91827364500/exam/problems/type/7?page=29&problemSetProblemId=91827370062) | 2017 ZJU School Contest | 1000 | implementation | My very first problem. |↵
