快速幂取模

    大数的幂的取模,还是非常有用的，即a^n%MOD,废话不多说，直接上代码：

#define LL long long int
LL POW(LL a,LL n,LL MOD){
    LL ret = 1;
    LL temp = a%MOD;
    while(n!=0){
        if(n%2==1) ret = (ret*temp)%MOD;
        n = n/2;
        temp = (temp *temp)%MOD;
    }
    return ret;
}

    至于原理嘛，一大牛的博客 http://blog.youkuaiyun.com/y990041769/article/details/22311889