NYOJ 333 mdd的烦恼&&NYOJ 291 LK的数学题

题目链接：http://acm.nyist.net/JudgeOnline/problem.php?pid=291   http://acm.nyist.net/JudgeOnline/problem.php?pid=333

思路：欧拉函数的应用，详解见这里：http://blog.csdn.net/once_hnu/article/details/6302868 好文章

直接贴代码：

#include <iostream>
#include <cstring>
using namespace std;

int euler(int x)
{
    int res = x;
    int a = x;

    for(int i=2;i*i<=a;i++)
    {
        if(a%i==0)
            res = res/i*(i-1);
        while(a%i==0)
            a /= i;
    }

    if(a>1)
        res = res/a*(a-1);
    return res;
}

int main()
{
    int n;
    int res;
    while(cin>>n)
    {
        cout<<euler(n)<<endl;
    }
    return 0;
}