1 #include <iostream> 2 #include <cstdio> 3 #include <algorithm> 4 using namespace std; 5 6 typedef long long LL; 7 const int MAXN = 1e4+5; 8 const LL INF = 1e15+5; 9 LL a[MAXN], sum[MAXN], ans[MAXN]; 10 11 int main() 12 { 13 int n, m; 14 while(cin>>n>>m) 15 { 16 for(int i=1; i<=n; i++) 17 scanf("%lld",&a[i]); 18 sort(a+1, a+1+n); 19 sum[0] = ans[0] = 0; 20 for(int i=1; i<=n; i++){ 21 sum[i] = sum[i-1] + a[i]; //前缀和 22 ans[i] = ans[i-1] + a[i]*a[i]; //^2的前缀和 23 } 24 double Min = INF; 25 for(int i=m; i<=n; i++){ 26 double tmp = (ans[i]-ans[i-m])-1.0*(sum[i]-sum[i-m])*(sum[i]-sum[i-m]) / m; 27 if(tmp < Min) 28 Min = tmp; 29 } 30 printf("%lld ", (LL)Min); //强行转不要小数点后面，防止四舍五入 31 } 32 return 0; 33 }