0x0002's blog

What happened with __int128_t?
By 0x0002, history, 12 days ago, In English

I was solving problem F of ABC just now. And I got passed with long long, but when I change the type into __int128_t, it got wrong answer in most of the cases. Why is that?

Passed with long long.

Wrong answer with int128.

Upd: It is said that __int128_t can not be the index of array. It may cause wrong answer. So it is always not a good idea to use things like #define int __int128_t.

Upd2: I just tested some other things on AtCoder about __int128_t, it seems template<typename> may work incorrectly with __int128_t. That's from my function read(). I searched for many times in Google but have not found why.

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11 days ago, # |
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11 days ago, # |
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11 days ago, # |
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10 days ago, # |
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10 days ago, # |
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10 days ago, # |
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I had some problem in problem B as well. If I use islower and isupper function to calculate lowercase and uppercase character count I get Wrong answer but passed without inbuilt function. Is it a problem with compiler?

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    10 days ago, # ^ |
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    My submission using islower and the same version of compiler got AC.

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    10 days ago, # ^ |
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    Google the cppreference for islower/isupper and check the output of islower('a')/isupper('A'). You'll be surprised how stupid it is.

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    10 days ago, # ^ |
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    islower and isupper are old C-style functions which return int with 0 for false and non-zero for true. So you had to write your code as any C programmer: !!islower(ch)

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    10 days ago, # ^ |
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    In fact I had the same problem due to this function and got a penalty. The fact is that this function does not return a bool result as we expected. Function islower() returns a non-zero value when it is a lowercase letter. You can check here for details.

    You can try the below code in custom test to see:

    #include <bits/stdc++.h>
using namespace std;

int main()
{
	ios::sync_with_stdio(0), cin.tie(0);
	cout << islower('A') << "\n"; // returns 0, it is not a lowercase letter
	cout << islower('a') << "\n"; // returns 2
	cout << islower('b') << "\n"; // returns 2
	cout << islower('z') << "\n"; // returns 2
	return 0;
}
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      10 days ago, # ^ |
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      Thanks a lot. On my machine it prints 0, 1, 1, 1 only. Probably different compilers have different implementations?

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        10 days ago, # ^ |
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        That is true because the standard only requires to return a non-zero value, but what it really returns may be different in different compilers.

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