[ABC332E] Lucky bag

#include <bits/stdc++.h>
using namespace std;
int n, d, x;
long double w[15], tot, dp[(1 << 15)][16], y;
int main() {
	cin >> n >> d;
	for (int i = 0; i < n; i ++ ) cin >> w[i], tot += w[i];
	tot /= (long double)d;
	for (int i = 0; i < (1 << n); i ++ , y = 0) {
		for (int j = 0; j < n; j ++ ) y += ((bool)(i & (1 << j))) * w[j];
		dp[i][1]=pow(y-tot,2);
		for(int j=2;j<=d;j++){
			dp[i][j]=dp[i][j-1]+dp[0][1];
			x=i;
			while(x>0){
				dp[i][j]=min(dp[i][j],dp[i-x][j-1]+dp[x][1]);
				x=(x-1)&i;
			}
		}
	}
	printf("%.15Lf", (dp[(1<<n)-1][d]/((long double)d)));
}