UVa 10006 - Carmichael Numbers

连接网址：https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=947

这一题的用到快速幂的求法：

 代码如下

AC代码：

# include <cstdio># include <cmath>using namespace std;typedef long long int LL;int mod_pow(int x, int n, int mod){if(n==0){return 1;}LL ans;ans=mod_pow(x, n/2, mod);ans=ans*ans%mod;if(n%2==1){ans=ans*x%mod;}return (int)ans;}int is_prime(int n){if(n<=1){return 0;}for(int i=2; i<=sqrt(n); i++){if(n%i==0){return 0;}}return 1;}int main(){int n, i, j, k, flage;while(scanf("%d", &n)){if(n==0){break;}if(is_prime(n)){printf("%d is normal.\n", n);continue;}flage=0;for(i=2; i<n; i++){if(mod_pow(i, n, n)!=i){flage=1;break;}}if(flage){printf("%d is normal.\n", n);}else{printf("The number %d is a Carmichael number.\n", n);}}return 0;}