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TLE when using C++11 and C++14 but AC using C++20
By pgiaminh8368, history, 3 years ago, In English

So I was doing this problem: https://codeforces.net/contest/1490/problem/F. And I got TLE when I use C++11: https://codeforces.net/contest/1490/submission/144339905 . and C++14: https://codeforces.net/contest/1490/submission/144338420 . but AC when using C++20: https://codeforces.net/contest/1490/submission/144339955 . Can anyone tell me why this is happening?

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3 years ago, # |
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Auto comment: topic has been updated by pgiaminh8368 (previous revision, new revision, compare).

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3 years ago, # |
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Change unordered_map to map . Time complexity of unordered_map on average is O(1) but it's worst case complexity is O(n)

https://codeforces.net/contest/1490/submission/144341577

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    3 years ago, # ^ |
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    Thank you.

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    3 years ago, # ^ |
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    So that mean access element of a unordered_map is faster in C++20?

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      3 years ago, # ^ |
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      This is a problem from a Div3 contest, which means that this contest had a 12 hours hacking phase. And unordered_map is known to be vulnerable to adversarially constructed input data, which may hit the worst case time complexity. C++20 isn't better. It's just a newer complier, which probably changed its unordered_map implementation a little a bit. So the old hacks need to be adjusted to successfully target it too. See https://codeforces.net/blog/entry/62393

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