2017-03-16 Codeforces 453A 概率期望,思维 UOJ 228(待补)

#include<bits/stdc++.h>
using namespace std;
#pragma comment(linker, "/STACK:102400000,102400000")
#define rep(i,a,b) for (int i=a;i<=b;i++)
#define per(i,b,a) for (int i=b;i>=a;i--)
#define mes(a,b)  memset(a,b,sizeof(a))
#define INF 0x3f3f3f3f
typedef long long ll;
const int N = 200005;

double fpow(double a, int b){double ans=1; for(;b;a=a*a,b>>=1)if(b&1)ans*=a; return ans;}
int main()
{
    int n, m;
    double ans=0;
    cin>>m>>n;
    rep(i,1,m) {
        ans+= (fpow(1.0*i/m, n)-fpow(1.0*(i-1)/m, n))*i;
    }
    printf("%.5f\n", ans);

    return 0;
}