階乗
(library/number/factorial.hpp)

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• Last update: 2026-01-07 21:05:45+09:00
• Include: #include "library/number/factorial.hpp"

階乗

できること

• $N!$ を求める

計算量

$O(N)$

使い方

long long fac = factorial(N);

Verified with

• 階乗のテスト (tests/number.factorial.test.cpp)

Code

#pragma once
long long factorial(int N) {
    long long res = 1;
    while (N > 0) res *= N--;
    return res;
}

#line 2 "library/number/factorial.hpp"
long long factorial(int N) {
    long long res = 1;
    while (N > 0) res *= N--;
    return res;
}

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