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Codeforces Round #405 — Div 2 : Problem B — regarding use of long long
By PeterParker, history, 8 years ago, In English

link — http://mirror.codeforces.com/contest/791/problem/B

I used the fact that each in each connected component there should be an edge between each pair of vertices. Hence the number of edges given should be equal to — summation x*(x-1)/2 for each connected component, where x = size of the connected component.

I used int and got a WA and when I replaced it with long long it got Accepted. Now my question is if the answer has to be "YES

" then sum should be <= 150000 (since that is the range of M in the question) so int should suffice then why did I get a WA?

WA link — http://mirror.codeforces.com/contest/791/submission/25610369 AC link — http://mirror.codeforces.com/contest/791/submission/25625604

Thanks in advance!

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8 years ago, # |
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int sz = 150000; sz*(sz-1) > INT_MAX So you need either declare sz as int64_t, or cast before the multiplication: (long long)sz * (sz-1)

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8 years ago, # |
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We can say that if answer for specified input is "YES", than overflow is impossible.
However, if answer is "NO", than component size can be big enough to cause overflow.

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