Shandong Province 8th ACM College Students Programming Contest G question sum of power fast power board sub-question

Title:

$\sum_{k=1}^n(i^m)mod(1000000000+7)$
Given n, m, find the value of this expression

analyze:

$1^m + 2^m + 3^m + 4^m + ........(n-1)^m + n^m$
Exponentiation operation, and also take the remainder of a large number, definitely fast power, board question

Code:

#include<iostream>
#include<algorithm>
#include<cstring>
#include<cmath>
#include<queue>
#include<stdio.h>
#define mod 1000000007
#define ll long long
using namespace std;

ll f(ll a,ll b)
{
    ll ans =1;
    a = a %mod;
    while(b)
    {
        if(b&1) ans = ans*a%mod;
        a = a*a%mod;
        b>>=1;
    }
    return ans;
}
int main()
{
    int n,m;
    cin >> n >> m;
    ll sum = 0;
    for(int i = 1; i <=n;i++)
    {
        sum = (sum+f(i,m))%mod;
    }
    cout << sum << endl;
    return 0;
}