What I learnt from Round 621 Div1+2

#	User	Rating
1	tourist	3985
2	jiangly	3814
3	jqdai0815	3682
4	Benq	3529
5	orzdevinwang	3526
6	ksun48	3517
7	Radewoosh	3410
8	hos.lyric	3399
9	ecnerwala	3392
9	Um_nik	3392

#	User	Contrib.
1	cry	169
2	maomao90	162
2	Um_nik	162
4	atcoder_official	160
5	djm03178	158
6	-is-this-fft-	157
7	adamant	155
8	Dominater069	154
8	awoo	154
10	luogu_official	151

Time: 11:29pm IST

Solved A
Solved B
Solved C
Couldn't think of D

-- Up-solve :

Solved A in 8 minutes. I think I could've solved it faster but my computer froze up. Nevertheless I should aim for sub 5 minute timings on A. I wonder do the people who solve it in 1-2 minutes even test their solutions? E.g. tourist who solved in 0:00 minutes. I used the coding format from 619's D problem and coded really nice solution. Happy to see up-solving paying off! O(n)
Really had fun time solving B. I imagined the circles intersecting as the rabbit's hops and felt pretty awesome after submitting the solution. I think elegant mathematics plus coding solutions is the best kind of computer science. Especially when you can visualize the concept in a 2D plane. I submitted a wrong answer which I knew in the back of my head was the case when he can hop in a single step to destination, guess I should think of all testcases before submitting answer. O(1)
First realize that solution will have either 1 letter hidden string or 2 letter. More than that isn't possible. Got this idea using some examples and mathematically too. I solved this then by storing results in 2D table. the table contained frequency of letters till that point. Then simple addition over this 26*n table for O(n) complexity gives answer. Really intuitive solution. See attached photo! photo
I had no idea how to work with D. I need to brush up on graph theory skills. Will watch William Fiset's Graph theory tutorials soon, then will try to solve as many questions as I can. Search for more resources.

What I Learnt

Binary Search+ segment trees was a possible solution for D. How I don't know but the fact that they can be used is amazing.
Calmly solving question with mathematical proof pays off.
Up-solving previous contest was reason I could perform well this time. Need to keep this streak.

--- New Things to learn:

I don't understand what is meant by Suffix Maximum array in D's editorial. Need to see some solutions.
Using emplace_back() function
Solving BFS questions to find shortest Distance from node to node.
Djikstra's implementation I need to try out.

---- Pending :

Read and try D

----Song of the contest

Thunderstruck by AC/DC :)

Comments (6)

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Tet

5 years ago, # |

-22

although the way you are treating the contest is a proper one, you should consider that publicly announcing your efforts is not always a good idea. why won't you write a blog about strategies to perform well in contests (after some research ofc) and how to upsolve them in a good way? :)

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