湖南多校对抗赛---Jerry's trouble

题目网址：http://acm.csu.edu.cn/OnlineJudge/problem.php?cid=2071&pid=9

Description

 Jerry is caught by Tom. He was penned up in one room with a door, which only can be opened by its code. The code is the answer of the sum of the sequence of number written on the door. The type of the sequence of number is

But Jerry’s mathematics is poor, help him to escape from the room.

Input

 There are some cases (about 500). For each case, there are two integer numbers n, m describe as above ( 1 <= n < 1 000 000, 1 <= m < 1000).

Output

 For each case, you program will output the answer of the sum of the sequence of number (mod 1e9+7).

Sample Input

4 1
5 1
4 2
5 2
4 3

Sample Output

10
15
30
55
100

题意很简单，快速幂完全可以解决，直接贴码

#include<iostream>
#include <cmath>
using namespace std; 
long long int q=1e9+7 ;
long long int ex(long long int a,long long int b){
       long long int ans;
        a=a%q;
        ans=1;
        while(b>0){
            if(b&1)//判断是否为奇数，相当于 if(b%2==1)
                ans=(ans*a)%q;
            a=(a*a)%q;
            b=b>>1;//二进制向右移一位，相当于 b=b/2;
        }
    return ans;
}
int main()
{
    long long int n,m;
    while(cin>>n>>m)
    {
        long long int sum=0;
        for(int i=1;i<=n;i++)
         sum=(sum+ex(i,m))%q;
          
    cout<<sum<<endl;
    }
    return 0;
}