POJ 2407 Relatives（欧拉函数的应用）

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题目链接：
http://poj.org/problem?id=2407

Relatives
Time Limit: 1000MS Memory Limit: 65536K
Total Submissions: 13726 Accepted: 6854
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
Source

Waterloo local 2002.07.01

本题是一道简单的欧拉函数的题目，要求的为phi(n)的值。直接最暴力的方法。

下面是AC代码：

#include<cstdio>#include<cstring>#include<algorithm>using namespace std;int phi(int n){    int rea=n;    for(int i=2;i*i<=n;i++)    {        if(n%i==0)        {            rea=rea-rea/i;            do                n/=i;            while(n%i==0);        }    }    if(n>1)    rea=rea-rea/n;    return rea;}int main(){    int n;    while(~scanf("%d",&n))    {        if(n==0)        {            break;        }        printf("%d\n",phi(n));    }    return 0;}

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