POJ2407(欧拉函数)

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Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 13598		Accepted: 6771

Description

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

裸的欧拉函数，因为n的数据比较大，不用筛选法打欧拉函数表，直接用公式：

　　

//2016.8.17
#include<iostream>
#include<cstdio>

using namespace std;

int phi(int n)
{
    int ans = n;
    for(int i = 2; i <= n; i++)
    {
        if(n%i==0)
        {
            ans -= ans/i;
            while(n%i==0)
                n /= i;
        }
        if(n == 1)break;
    }
    return ans;
}

int main()
{
    int n;
    while(cin>>n&&n)
    {
        cout<<phi(n)<<endl;
    }

    return 0;
}