数论-欧拉函数

#include<cmath>
#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;
int main(void)
{
    int n;
    while(~scanf("%d",&n))
    {
        int ans = n;
        int m = sqrt(n+0.5);
        for(int i = 2; i <= m; i++)
        {
            if(n==1)
                break;
            if(n%i==0)
            {
                ans = ans/i*(i-1);
                while(n%i==0)
                     n = n / i ;
            }
        }
        if(n!=1)
            ans = ans/n*(n-1);
        printf("%d\n",ans);
    }
    return 0;
}

#include<cmath>
#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;
const int maxn = 100;
int euler[maxn];
void Init()
{
     euler[1]=1;
     for(int i = 2; i <= maxn; i++)
       euler[i]=i;
     for(int i = 2; i <= maxn; i++)
        if(euler[i]==i)
           for(int j = i; j <= maxn; j+=i)
              euler[j]=euler[j]/i*(i-1);//先进行除法是为了防止中间数据的溢出
}

int main(void)
{
    Init();
    for(int i = 1; i <= maxn; i++)
    {
        printf("%d %d\n",i,euler[i]);
    }
    return 0;
}

#include<cmath>
#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;
const int maxn = 100;
int book[maxn];
int prime[maxn];
int phi[maxn];
int num;
void Init() 
{
    memset(book, 0, sizeof (book));
    phi[1] = 1;
    book[0] = 1; 
    book[1] = 1;
    for (int i = 2; i <= maxn; i++) 
    {
        if (book[i]==0) 
        {
            prime[num++] = i;
            phi[i] = i - 1;
        }
        for (int j = 0; j < num; j++)
         {
            int p = prime[j];
            if (i * p > maxn) 
                break;
            book[i * p] = 1;
            phi[i * p] = (i % p == 0 ? phi[i] * p : phi[i] * (p - 1));
            if (i % p == 0) 
                break;
        }
    }
}
int main(void)
{
    Init();
    for(int i = 1; i < maxn; i++)
        printf("%d %d\n",i,phi[i]);
    return 0;
}