A的B次幂

Description

给出两个正整数A和B

请输出A的B次幂

结果可能很大，请对1000000007求模

Input

A和B，两个整数均不大于10^18

Output

A的B次幂对1000000007求模

 

Sample Input 1 

2 2

Sample Output 1

4

Sample Input 2 

2 10

Sample Output 2

1024

快速幂：其实我也没搞明白。emmmmmmm等我搞明白了再说吧。献上代码！

#include<iostream>
using namespace std;
long long cu(long long a, long long b) {
    long long s = 1;
    while(b > 0) {
        if(b%2 == 1) {
            s = s % 1000000007;
            a = a % 1000000007;
            s = s * a;
        }
        a = a % 1000000007;
        a = a * a;
        b = b / 2;
    }
    return s % 1000000007;
}
int main()
{
    long long a, b;
    cin >> a >> b;
    cout << cu(a, b);
}