数论之求欧拉函数

简单的求欧拉函数的值，留下来做个模板。。。。。。。。。。

题目：

Given n, a positive integer, how many positive integers less than n are relatively prime to n? Two integers a and b are relatively prime if there are no integers x > 1, y > 0, z > 0 such that a = xy and b = xz.

Input

There are several test cases. For each test case, standard input contains a line with n <= 1,000,000,000. A line containing 0 follows the last case.

Output

For each test case there should be single line of output answering the question posed above.

Sample Input

7 12 0

Sample Output

6 4

ac代码：

#include <iostream> #include <cstdio> #include <cmath> using namespace std; long long euler(long long y){ int m=(int)sqrt(y+0.5); int ans=y; for(int i=2;i<=m;++i){ if(y%i==0){ ans=ans/i*(i-1); while(y%i==0) y/=i; } } if(y>1) ans=ans/y*(y-1); return ans; } int main() { long long n; while(cin>>n&&n){ long long x=euler(n); cout<<x<<endl; } }