UPD: We have changed contest duration from 3 hours to 3.5 hours.

We will hold UOJ Easy Round #13 contest! You will be given 4 problems to be solved in 3.5 hours.

• Contest link: https://uoj.ac/contest/106
• Start Time: https://www.timeanddate.com/worldclock/fixedtime.html?iso=20260404T1900&p1=33&ah=3
• Writers: Comentropy, pp_orange, jiaosiyuan, Gellyfish
• Testers: Crysfly, hos.lyric
• Duration: 3.5 hours
• Difficulty: CF Div 1.5/ARC++
• The point values: 100-100-100-100

The contest will follow the IOI rules: Each problem can be submitted up to 50 times, and scores can be viewed in real-time. All the problems will have subtasks, the final score will be based on the highest-scoring submission.

You can see the scoreboard during the contest.

The contest is rated for everyone, you will be count as rated only if you opened at least one problem.

We are looking forward to your participation!

Goodbye, Yisi!

We will host the Goodbye Yisi contest! The contest contains $$$6$$$ problems to be solved in $$$5$$$ hours.

This contest serves as our annual Chinese Lunar New Year special event, marking the farewell to the Year of Yisi and welcoming a brand new year.

• Contest link: https://uoj.ac/contest/105
• Start Time: https://www.timeanddate.com/worldclock/fixedtime.html?iso=20260215T1300&p1=33&ah=5
• Writers: Sunset1028, le0n, Flamire, Kubic
• Testers: hos.lyric, Crysfly
• Duration: 5 hours
• Difficulty: CF Div.1+
• The point values: 100-100-100-100-100-100

The contest will follow the IOI-style rules: Each problem can be submitted up to 50 times, and scores can be viewed in real-time. All the problems will have subtasks, the final score will be based on the highest-scoring submission.

We are looking forward to your participation!

UPD: Congratulation to the winners!

1. BreakPlay
2. jiangbowen
3. 275307894a
4. strapple
5. larsr

We will hold UOJ Round #33 contest! You will be given 4 problems to be solved in 4 hours.

• Contest link: https://uoj.ac/contest/104
• Start Time: https://www.timeanddate.com/worldclock/fixedtime.html?iso=20260201T1800&p1=33&ah=4
• Writers: tianbincheng, Gellyfish, JoesSR, crsfafa
• Testers: Flamire, Tony2_CF, hos.lyric
• Duration: 4 hours
• Difficulty: CF Div.1
• The point values: 100-100-100-100

The contest will follow the IOI rules: Each problem can be submitted up to 50 times, and scores can be viewed in real-time. All the problems will have subtasks, the final score will be based on the highest-scoring submission.

You can see the scoreboard during the contest.

The contest is rated for everyone, you will be count as rated only if you opened at least one problem.

We are looking forward to your participation!

Hi, everyone.

The first stage of the IOI 2026 China Team Selection has ended today. The top 48 participants from the 2025 National Olympiad in Informatics (NOI) will compete for a spot on the Chinese national team for IOI 2026.

The rule of selecting CHN team this year:

• Homework (10%). The participants are asked to choose 4 tasks for homework and complete 60 tasks of them.
• First stage (CTT; 54%; Dec 2, 2025 — Dec 4, 2025): three contests in classic olympiad format, where each contest worthes 18% of the score. Top 30 participants will advance to the final stage.
• Final stage (CTS; 36%; Feb 10, 2026 — Feb 12, 2026): two contests in classic olympiad format, where each contest worthes 18% of the score.

The current scoreboard can be found here. Tasks of the first round can be found here

UPD1: The Day1 contest of CTS have ended.

UPD2: The Day2 contest of CTS have ended. Kevin114514,fake_banana,Z-301,NKheyuxiang,flying,Flamire will enter the thesis defense stage.

We will hold UOJ Long Round #3 contest!

The contest will run for 60 hours, spanning the entire weekend. You will be given 6 problems. (so it will be like a PA-Runda 5 contest XD)

Overall, the difficulty should be a bit easier than previous ULR contests (?). Everyone is welcome to come and enjoy solving them without worry.

• Contest link: https://uoj.ac/contest/103
• Start Time: https://www.timeanddate.com/worldclock/fixedtime.html?iso=20251121T1000&p1=33
• Writers: Coffee_zzz, _istil, OIer1048576, Tony2_CF, ODT
• Testers: Flamire, zjy2008, hos.lyric, XY_Eleven, crsfafa, Urd-
• Duration: 60 hours
• Difficulty: CF Div.1+
• The point values: 100-100-100-100-100-100

Additionally, one of the problems will be judged with WASM-judge support. Special thanks to aberter0x3f. (Contestants may simply treat this as more precise time/space computation during judging, there is almost no perceptible difference during the contest. For technical details, see the post at https://yzy1.blog.uoj.ac/blog/9339.)

The contest will follow the IOI rules: Each problem can be submitted up to 128 times, and scores can be viewed in real-time. All the problems will have subtasks, the final score will be based on the highest-scoring submission.

You can see the scoreboard during the contest.

The contest is rated for everyone, but the rating change will only be 1/128 of a normal contest. So feel free to join just for fun!

We are looking forward to your participation!

UPD: Congratulation to the winners!

1. maspy
2. jiangbowen
3. Max_s_xaM
4. feecle6418
5. operator_

The editorials will be updated here.

We will hold UOJ Round #32 contest! You will be given 3 problems to be solved in 4 hours.

• Contest link: https://uoj.ac/contest/102
• Start Time: https://www.timeanddate.com/worldclock/fixedtime.html?iso=20251019T1800&p1=33&ah=4
• Writers: CommonAnts, Alan_dong, b6e0
• Testers: Flamire, Gellyfish, zjy2008, hos.lyric
• Duration: 4 hours
• Difficulty: CF Div.1+
• The point values: 100-100-100

The contest will follow the Pretest-IOI rules: During contest, every submission will only be judged on the pretests. All submissions will be rejudged on the final tests after contest. You can submit a problem at most 50 times. All the problems will have subtasks, the final score will be based on the last submission.

You can see the scoreboard during the contest.

The contest is rated for everyone, you will be count as rated only if you opened at least one problem.

We are looking forward to your participation!

We will hold UOJ NOI Round #9 contest!

This would be a simulation contest for Chinese NOI, with 2 days of 3-problem contest. Be free to participate if you are preparing for IOI, or other IOI-like contests.

Final ranking will be based on the total score across all three rounds. In the case of a tie, the total penalty time from 2 main contest days will be used as a tiebreaker.

• Day 0 (unrated) link: https://uoj.ac/contest/99 (Start Time: https://www.timeanddate.com/worldclock/fixedtime.html?iso=20250706T1900&p1=33&ah=0&am=30)
• Day 1 link: https://uoj.ac/contest/100 (Start Time: https://www.timeanddate.com/worldclock/fixedtime.html?iso=20250707T0830&p1=33&ah=5)
• Day 2 link: https://uoj.ac/contest/101 (Start Time: https://www.timeanddate.com/worldclock/fixedtime.html?iso=20250708T0830&p1=33&ah=5)
• Duration: 5 hours
• Difficulty: Chinese NOI
• The point values: 100-100-100-100-100-100-100

The writers & testers will be revealed after Day0 contest.

Writers: Crysfly, myee, EvenImage, registeretsiger, Gellyfish

Testers: JoesSR, Kubic, zhoukangyang

The contest will follow the Pretest-IOI rules: During contest, every submission will only be judged on the pretests. All submissions will be rejudged on the final tests after contest. You can submit a problem at most 50 times. All the problems will have subtasks, the final score will be based on the last submission.

You can't see the scoreboard during the contest.

The contest is rated for everyone, you will be count as rated only if you opened at least one problem.

We are looking forward to your participation!

We will hold UOJ Round #31 contest! You will be given 3 problems to be solved in 4 hours.

• Contest link: https://uoj.ac/contest/98
• Start Time: https://www.timeanddate.com/worldclock/fixedtime.html?iso=20250629T1800&p1=33&ah=4
• Writers: Graygoo_401, Coffee_zzz, return20071007, pp_orange
• Testers: zhoukangyang, Crysfly, Gellyfish
• Duration: 4 hours
• Difficulty: CF Div.1+
• The point values: 100-100-100

The contest will follow the Pretest rules: During contest, every submission will only be judged on the pretests (in the problem attachments). All submissions will be rejudged on the final tests after contest. All the problems will have subtasks, the final score will be based on the last submission.

The contest is rated for everyone, you will be count as rated only if you opened at least one problem.

We are looking forward to your participation!

UPD: Congratulation to the winners!

1. maroonrk
2. hos.lyric
3. jiangbowen
4. BreakPlay
5. Flamire

The editorials will be posted here.

We will hold UOJ Round #30 contest! You will be given 3 problems to be solved in 4 hours.

Recently, the Flea National Games has begun and a marathon competition will be held between "Lightning Fleas" and the rising "Quantum Fleas". Can you solve three problems about this competition?

• Contest link: https://uoj.ac/contest/97
• Start Time: https://www.timeanddate.com/worldclock/fixedtime.html?iso=20250510T1800&p1=33&ah=4
• Writers: pp_orange, JoesSR, crazy_sea
• Testers: Crysfly, BreakPlay
• Duration: 4 hours
• Difficulty: CF Div.1+
• The point values: 100-100-100

The contest will follow the Pretest rules: During contest, every submission will only be judged on the pretests (in the problem attachments). All submissions will be rejudged on the final tests after contest. All the problems will have subtasks, the final score will be based on the last submission.

The contest is rated for everyone, you will be count as rated only if you opened at least one problem.

We are looking forward to your participation!

UPD: Congratulation to the winners!

1. hos.lyric
2. cat_of_Nesraychan
3. Z-301
4. Kevin114514
5. jiangbowen

The editorials will be posted here.

We will hold UOJ Easy Round #12 contest! You will be given 3 problems to be solved in 3 hours.

Recently, Flea Kingdom has been attempting to build a smart power grid for their nation. Can you help Volt accomplish the task of constructing the power grid?

• Contest link: https://uoj.ac/contest/95
• Start Time: https://www.timeanddate.com/worldclock/fixedtime.html?iso=20250316T1900&p1=33&ah=3
• Writers: Gellyfish, Crysfly, Kubic
• Duration: 3 hours
• Difficulty: CF Div.1.5 / ARC
• The point values: 100-100-100

The contest will follow the Pretest rules: During contest, every submission will only be judged on the pretests (in the problem attachments). All submissions will be rejudged on the final tests after contest. All the problems will have subtasks, the final score will be based on the last submission.

The contest is rated for everyone, you will be count as rated only if you opened at least one problem.

We are looking forward to your participation!

UPD: Congratulation to the winners!

1. hos.lyric
2. cat_of_Nesraychan
3. umbrella-leaf
4. xuanxuan001
5. paul2008

We will hold UOJ Round #29 contest! The contest contains $$$3$$$ problems to be solved in $$$4$$$ hours.

King Volt of the Fleas decided to establish a brand-new academic discussion community called "Flea Universe". However, during the process of building the community, Volt encountered some technical difficulties. Can you help Volt overcome these difficulties and contribute to creating a new academic discussion community for the Flea Kingdom?

• Contest link: https://uoj.ac/contest/94
• Start Time: https://www.timeanddate.com/worldclock/fixedtime.html?iso=20250216T1800&p1=33&ah=4
• Writers: Gellyfish, zhoukangyang, dXqwq, xyf007
• Testers: yaoxi, registeretsiger
• Duration: 4 hours
• Difficulty: like CF Div.1 contests (maybe slightly harder)
• The point values: 100-100-100

The contest will follow the Pretest rules: During contest, every submission will only be judged on the pretests (in the problem attachments). All submissions will be rejudged on the final tests after contest. All the problems will have subtasks, the final score will be based on the last submission.

The contest is rated for everyone, you will be count as rated only if you opened at least one problem.

We are looking forward to your participation!

UPD1: The contest will start in 40 minutes.

UPD2: Congratulations to the winners!

1. BreakPlay
2. hhoppitree
3. jiangbowen
4. zjy2008
5. cmk666

Goodbye, Jiachen!

We will host the Goodbye Jiachen contest! The contest contains $$$5$$$ problems to be solved in $$$5$$$ hours.

The year 2024 marks the end of the Chinese Lunar Jiachen Dragon Year, with Lunar New Year's Eve symbolizing its conclusion. The upcoming year will be the Yisi Snake Year, where the snake represents wisdom and the cycle of rebirth.

As time passes, UOJ continues to embrace new milestones. From Goodbye Jiawu to Goodbye Jiachen, we have witnessed UOJ's growth and changes over the past decade.

This contest will take you into the world of Poker Kingdom. You will face challenges alongside five poker card characters, writing your own chapter of victory.

• Contest link: https://uoj.ac/contest/93
• Start Time: https://www.timeanddate.com/worldclock/fixedtime.html?iso=20250127T1300&p1=33&ah=5
• Writers: Gellyfish, miao22, Melania
• Testers: zhoukangyang, Crysfly, registeretsiger, yaoxi
• Duration: 5 hours
• Difficulty: like CF Div.1 contests (maybe slightly harder)
• The point values: 100-100-100-100-100

The contest will follow the IOI-style rules: Each problem can be submitted up to 50 times, and scores can be viewed in real-time. All the problems will have subtasks, the final score will be based on the highest-scoring submission.

We are looking forward to your participation!

Q&A

Q1: What can I do if I can't understand Chinese?

You can change the website to English at the bottom of the website.

We don't have English statements for problems now, sorry! But ChatGPT may be helpful for translation.

UPD: Congratulations to the winners!

1. BreakPlay
2. hhoppitree
3. PersistentLife
4. hos.lyric
5. qiuzx

Hello everyone! As you might know, World Tour Finals 2022 will take place on Sep 8th and 9th in Tokyo. Let's share your predictions here!