atcoder_official's blog

By atcoder_official, history, 4 months ago, In English

We will hold UNIQUE VISION Programming Contest 2024 Spring(AtCoder Beginner Contest 346).

We are looking forward to your participation!

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4 months ago, # |
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Hope to solve a,b,c,d,e.

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4 months ago, # |
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I hope all problems are Div3 type only.

Atcoder Beginner contest == Codeforces Div 3

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4 months ago, # |
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Hope to solve ABCDEF.

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4 months ago, # |
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Hope to solve ABCDE. I hope I won't be hacked this time

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4 months ago, # |
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Hope to solve ABCD

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Hope to solve ABCDE

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4 months ago, # |
  Vote: I like it +64 Vote: I do not like it

Problem E is almost the same as 2023 Chinese NOI Spring Test Problem A. 涂色游戏 (paint), and is an easy version of LGR-162-Div.3 Problem D. 头 which I coauthored.

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4 months ago, # |
Rev. 2   Vote: I like it +5 Vote: I do not like it

Please, can somebody tell me why this fails on F it literally binary searches the first left position to place "K" characters for every character in T. These contests are literally implementation only and I hate every minute of it.

16xAC 37xWA Link

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4 months ago, # |
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I deducted the n^2 brute force solution mentioned at the end of G's editorial in 5 min, but just can't find a way to use a data structure to optimize it:( maybe i just ain't Chinese enough:P

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    4 months ago, # ^ |
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    registered 5 months ago and already master, i am pretty sure that you are chinese D:

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    4 months ago, # ^ |
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    In sweepline you add and remove segments. Use a lazy segment tree to maintain the number of segments that cover each point. Adding is += 1 on a range and removing is -= 1 on a range. Query union length after each operation. It is n minus the count of zeros. The count of zeros is the count of minimums if the minimum is zero and zero otherwise code

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      4 months ago, # ^ |
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      yeah i figured out the sweepline part with ease but couldnt think of the sgt part...

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4 months ago, # |
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wtf is F, I cannot understand why this fails: binsearch on K, for checking each character, binsearch again on how far we have to go

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    4 months ago, # ^ |
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    I did the same thing but idk where I'm getting 2 WAs from.

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      4 months ago, # ^ |
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      For me, the 2 WAs was because of limits of binary search. Initially I put high to be 1e18 but I don't know why this was causing 2 WAs. Changing it to n*(size of s) worked. 1e18 probably caused overflow somewhere i don't know why. But even 1e17 limit which is 1e12*1e5 was causing 1 WA.

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        4 months ago, # ^ |
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        The upper bound of length is (n*(size of s))/(size of t),if you take a take k such that k*(size of t) > 2^63,it can overflow.

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          4 months ago, # ^ |
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          ohh yeah, wierd 1e17 failed, but n*(size of s) passed and I don't think it is possible that they did not put n = 1e12 and |s| = 1e5 testcase. Maybe i got lucky lol.

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        4 months ago, # ^ |
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        Try this test: n = 1

        s = a

        t = aaaaa

        ans = 0

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          4 months ago, # ^ |
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          Me:

          1
          aa
          aa
          

          The answer is 1 and my code output 0. Now I fixed the code by this test.

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      4 months ago, # ^ |
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      Had the same issue where I put 1e18 and got 2 WAs. Turns out this is because of overflows on long longs when you do the binary search. Switching to bigint made it AC.

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        4 months ago, # ^ |
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        Me too,I used "long long" at first and got "WA",and I used "unsigned long long" and got "AC".

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    4 months ago, # ^ |
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    This works, i did the same thing, code -Link

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    4 months ago, # ^ |
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    Did the same and failed 37 WA lol. It's a shit problem tbh just implementationforces.

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      4 months ago, # ^ |
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      It may be beneficial for you to focus on improving your implementation or at least debugging skills. It's unfortunate to miss out on some good points because of silly bugs but it's on you.

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4 months ago, # |
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first time with Corona Virus (just to D sadness)say no more go to sleep

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4 months ago, # |
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Is F binary search on answer and for each search, you binary search to find when you have enough letters? My solution was n(logn^2) but it TLEs on a couple cases.

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4 months ago, # |
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Today was a bit on easier side..could solve upto E :)

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How to solve D using DP ?

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    4 months ago, # ^ |
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    you can do it with prefix sum

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      4 months ago, # ^ |
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      can u explain prefix sum approach?

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        4 months ago, # ^ |
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        idea
        code
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          4 months ago, # ^ |
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          sorry i really not getting your ideas can you explain more?

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            4 months ago, # ^ |
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            you have to make string such that s[i] == s[i + 1] for exactly one i and the const should be minimum the idea is calculate cost for all possible i for both cases s[i] == 1 and s[i] == 0

            suppose we choose s[i] == 0 and i is odd
            now on the left <= i
            all 1's should occur at even position
            all 0's should occur at odd position
            
            on right >= i + 1
            all 1's should occur at odd position
            all 0's should occur at even position
            
            total cost = cost of making left + cost of making right
            
            similarly do it for s[i] == 1
            
            and the ans will be min cost considering all possible i for both cases
            
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    4 months ago, # ^ |
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4 months ago, # |
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how to do D with dp?

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    4 months ago, # ^ |
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    $$$dp[pos][prev][count]$$$

    pos = current position

    prev= value of previous character

    count = min( 2 ,count of $$$1 \le i \le n-1$$$ where $$$s_i=s_i+1$$$)

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      4 months ago, # ^ |
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      for s[i] == s[i + 1] you just have to make sure either on the left for all k <= i parity of k == s[k] and on the right k >= i + 1 parity of k != s[k] or vice versa

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      4 months ago, # ^ |
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      i am getting wrong on 3 test cases. What have i missed?

      Code

      https://atcoder.jp/contests/abc346/submissions/51621500

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4 months ago, # |
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Solved all problems after so many contests, thank you for the contest

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4 months ago, # |
Rev. 5   Vote: I like it +10 Vote: I do not like it

I have an edge case for problem F.

testcase :

2

aaa

aa

expected output : 3

But output of my accepted code for this testcase is 1. So, my code should got WA verdict. But my code got accepted.

Here is my submission link : https://atcoder.jp/contests/abc346/submissions/51615694

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    4 months ago, # ^ |
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    Mine gives 3 lmao but still fails 37 cases. Can you try finding a counter for mine please?

    Submission

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      4 months ago, # ^ |
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      Take a look at Ticket 17424 from CF Stress for a counter example.

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        4 months ago, # ^ |
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        Thanks so much, I rounded one division down instead of up and messed up whole problem. :(

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      4 months ago, # ^ |
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      10 yyqml y answer should be 20 , your code gives 21

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        4 months ago, # ^ |
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        I got it, I rounded down division in one place instead of up. Thanks.

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4 months ago, # |
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I have a question for problem B. I solved it in this manner: https://atcoder.jp/contests/abc346/submissions/51573486.

I was curious though, what if the values of W and B are very large(upto 1e18 or 1e9). In that case how will I be able to approach the problem. Is that even solvable? I am not able to think of any solution .Any help would be appreciated. Thank you

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    4 months ago, # ^ |
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    Iterate over all starting points on the string and calculate how many strings you need for b since there are less occurences of b in the strings and then iterate over the remainder of the string.

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    4 months ago, # ^ |
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    yes

    how
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In B, how answer is "No" for W=7,B=5???

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4 months ago, # |
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absolutely interesting problem, G is hard but the tutorial is very clear.

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This Round was really amazing. I really enjoyed this round. The problems are very good

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4 months ago, # |
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Can anybody tell me why this code is giving RE in problem D. Link to solution: https://atcoder.jp/contests/abc346/submissions/51621300

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    4 months ago, # ^ |
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    Because your memory usage (3628612 KB) is greater than the memory limit (1024 MB). You probably run into bad_alloc

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      4 months ago, # ^ |
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      Can you tell why my code memory usage exceeds, as it is a simple dp solution.

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        4 months ago, # ^ |
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        I modified your submission into this Now it passes. The idea is to change string to string& in the function declaration.

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          4 months ago, # ^ |
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          Ohh shit man silly error. Thanks for your help.

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4 months ago, # |
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For D, I don't really get why this (http://atcoder.jp/contests/abc346/editorial/9651) is a correct solution. I don't understand how the answer is computed. I thought that if n is even, then the series first character must be different than the last character, so ans = min(ans, l0[i] + g1[i]) and ans = min(ans, l1[i] + g0[i]). If n is odd then the first and last characters are the same so ans = min(ans, l0[i] + g0[i]) and ans = min(ans, l1[i], g1[i]).

However I see that doesn't matter for the solution. I'm confused — can anybody explain it to me?

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    4 months ago, # ^ |
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    Here is the crux of the idea
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      4 months ago, # ^ |
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      Thank you! Everything is clear to me until the last step. For the last point, isn't the validity of a pair out of the 4 based on whether n is even or odd? What i am saying is that if n is even, then (pref0, suf0) and (pref1, suf1) are valid, and if n is odd, then (pref0, suf1) and (pref1, suf0) are valid. What am i missing here?

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        4 months ago, # ^ |
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        Yes, thats the correct interpretation of the last line.

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can i do problem G by taking number of elements to right until not finding current element and left and add to result like res+=l*r is this wrong approach please help me

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    4 months ago, # ^ |
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    You end up with lots of duplicate pairs. Think about a simple case [3, 4], you gonna count pair (1, 2) twice according to what you say.

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When will the test data for ABC344/ABC345/ABC346 be uploaded? I need it now, thanks!

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There is something wrong with my submission on F. Can anyone help me? Many thanks. https://atcoder.jp/contests/abc346/submissions/51648515

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    4 months ago, # ^ |
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    Your soln fails on following testcase
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      4 months ago, # ^ |
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      My problem has been solved now. Thank you for your reply.

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This solution fails on only one test case could someone help? https://atcoder.jp/contests/abc346/submissions/51666225