SGU102 Coprimes

题目大意

输入一个正整数N
输出小于等于N并且与N互素的正整数的个数

算法思路

欧拉函数

时间复杂度: O(N‾‾√)

代码

/** * Copyright (c) 2015 Authors. All rights reserved. *  * FileName: 102.cpp * Author: Beiyu Li <[e-mail]> * Date: 2015-05-21 */#include <bits/stdc++.h>using namespace std;#define rep(i,n) for (int i = 0; i < (n); ++i)#define For(i,s,t) for (int i = (s); i <= (t); ++i)#define foreach(i,c) for (__typeof(c.begin()) i = c.begin(); i != c.end(); ++i)typedef long long LL;typedef pair<int, int> Pii;const int inf = 0x3f3f3f3f;const LL infLL = 0x3f3f3f3f3f3f3f3fLL;int main(){        int n;        scanf("%d", &n);        int res = n;        for (int i = 2; i * i <= n; ++i) if (n % i == 0) {                res = res / i * (i - 1);                while (n % i == 0) n /= i;        }        if (n != 1) res = res / n * (n - 1);        printf("%d\n", res);        return 0;}

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