LeetCode - Best Meeting Point

BestMeetingPoint.java

// A group of two or more people wants to meet and minimize the total travel distance. You are given a 2D grid of values 0 or 1, where each 1 marks the home of someone in the group. The distance is calculated using Manhattan Distance, where distance(p1, p2) = |p2.x - p1.x| + |p2.y - p1.y|.

// For example, given three people living at (0,0), (0,4), and (2,2):

// 1 - 0 - 0 - 0 - 1
// |   |   |   |   |
// 0 - 0 - 0 - 0 - 0
// |   |   |   |   |
// 0 - 0 - 1 - 0 - 0
// The point (0,2) is an ideal meeting point, as the total travel distance of 2+2+2=6 is minimal. So return 6.

// find the median
public int minTotalDistance(int[][] grid) {
    if(grid == null || grid.length == 0 || grid[0].length == 0) return 0;
    List<Integer> rows = new ArrayList<Integer>();
    List<Integer> cols = new ArrayList<Integer>();
    
    for(int i = 0; i < grid.length; i++){
        for(int j = 0; j < grid[0].length; j++){
            if(grid[i][j] == 1){
                rows.add(i);
                cols.add(j);
            }
        }
    }
    
    Collections.sort(cols);
    return getMinDistance(rows, rows.get(rows.size() / 2)) + getMinDistance(cols, cols.get(cols.size() / 2));
}

private int getMinDistance(List<Integer> lst, int origin){
    int res = 0;
    for(int num : lst){
        res += Math.abs(num - origin);
    }
    return res;
}


// without the median
public int minTotalDistance(int[][] grid) {
    if(grid == null || grid.length == 0 || grid[0].length == 0) return 0;
    List<Integer> rows = new ArrayList<Integer>();
    List<Integer> cols = new ArrayList<Integer>();
    
    for(int i = 0; i < grid.length; i++){
        for(int j = 0; j < grid[0].length; j++){
            if(grid[i][j] == 1){
                rows.add(i);
                cols.add(j);
            }
        }
    }
    
    Collections.sort(cols);
    return getMinDistance(rows) + getMinDistance(cols);
}

private int getMinDistance(List<Integer> lst){
    int res = 0, left = 0, right = lst.size() - 1;
    while(left < right){
        res += lst.get(right--) - lst.get(left++);
    }
    return res;
}