鞍山邀请赛 部分题

http://acm.hdu.edu.cn/showproblem.php?pid=5073    

题意：给你n个行星，移动k个行星，绕他们的质心速度变得更大，使得这些行星的速度变得更大，那么就要使得

I的值更小即可，

#include<cstdio>#include<cstring>#include<iostream>#include<algorithm>using namespace std;double zb[70100];double sum[70005];double s[70005];int main(){    int t,n,m;    scanf("%d",&t);    while(t--){        scanf("%d%d",&n,&m);        for(int i = 1;i <= n;i++)            scanf("%lf",&s[i]);        if(m >= n - 1) {printf("0\n");continue;}        sort(s+1,s+n+1);        zb[0] = 0;sum[0] = 0;        for(int i = 1;i <= n;i++){            zb[i] = zb[i-1] + s[i];//预处理前n项和；            sum[i] = sum[i-1] + s[i]*s[i];//预处理前n项平方和；        }        double zx1 = zb[n]/(n-m);        double _min = sum[n] + (n-m) * zx1 * zx1 - 2 * zx1 * zb[n];//注意不移动的时候他的Ｉ值        for(int i = n-m;i <= n ;i++)//苦逼的边界无限的WA        {            double tmp = zb[i] - zb[i-n+m];            double r = tmp/(n-m);            double k = sum[i] - sum[i-n+m];            double ret = k + (n-m) * r * r - 2 * r * tmp;            _min = min(ret,_min);        }        printf("%.10lf\n",_min);    }    return 0;}