UVA 10006 Carmichael Numbers

素數打表+快速冪取模

先判斷是不是素數，不是就直接結束，不然會超時...

#include <iostream>
#include<cstring>
#include<stdio.h>
#include<cmath>
#define maxn 65010
using namespace std;
int vis[maxn];

void sieve()
{
    int m = (int)sqrt(maxn + 0.5);
    memset(vis,0,sizeof vis);
    for(int i = 2;i <= m;i++) if(!vis[i])
        for(int j = i * i;j <= maxn;j+=i) vis[j] = 1;
}

long long quick_mod(long long a,long long b,long long m)
{
    long long ans = 1;
    while(b)
    {
        if(b&1)
        {
            ans = (ans * a)%m;
        }
        b = b>>1;
        a = a * a % m;
    }
    return ans;
}

int main()
{
    sieve();
    long long n;
    long long ans;
    while(scanf("%lld",&n),n)
    {
        int ok = 1;
        if(!vis[n]) {printf("%lld is normal.\n",n);continue;}
        for(long long i = 2;i <= n - 1;i++)
        {
            ans = quick_mod(i,n,n);
            if(ans != i) {ok = 0;break;}
        }
        if(ok ) printf("The number %lld is a Carmichael number.\n",n);
        else printf("%lld is normal.\n",n);
    }
    return 0;
}