int minimum(int M, vector <int> heights)    {        sort(heights.begin(),heights.end());        int minFloor = 10000;        for(int i = heights.size()-1; i >=M-1; -- i){            int floor = 0;            for(int j = 0; j < M; ++j) floor +=heights[i]-heights[i-j];            minFloor =min(minFloor,floor);        }        return minFloor;    }