题目描述

样例

#include<cmath>
#include<cstdio>
#include<iostream>
#include<algorithm>
using namespace std;
const int N=500005;

int a[N];
double b[N];

int main(){
    int n;
    double s;
    scanf("%d%lf",&n,&s);
    double avg=s/n;
    for(int i=0;i<n;i++){
        scanf("%d",&a[i]);
    }
    sort(a,a+n);

    double marg=0.0;
    int i;
    for(i=0;i<n;i++){
        if(a[i]<=avg){
            marg+=abs(avg-a[i]);
            b[i]=(double)(a[i]);
        }
        else{
            break;
        }
    }

    for( ;i<n;i++){
        if(abs(a[i]-avg)<marg/(n-i)){
            marg-=abs(a[i]-avg);
            b[i]=(double)(a[i]);
        }
        else{
            break;
        }
    }
    int j=i;
    for( ;i<n;i++){
        b[i]=avg+marg/(n-j);
    }

    double sum=0;

    for(i=0;i<n;i++){
        sum+=(b[i]-avg)*(b[i]-avg);
    }

    sum=sqrt(sum/n);

    printf("%.4lf",sum);

    return 0;
}