296.Best Meeting Point

https://leetcode.com/problems/best-meeting-point/

因为是曼哈顿距离，所以直接压缩成一维的问题。
一维的grid里，最佳点是中间的点，如果为奇数则为中点，偶数则为中点中的任意一个。

class Solution {
public:
    int minTotalDistance(vector>& grid) {
        int m = grid.size();
        if(m == 0) return 0;
        int n = grid[0].size();
        if(n == 0) return 0;
        vector y;
        vector x;
        
        //init
        for(int i = 0; i < m; i++) {
            for(int j = 0; j < n; j++) {
                if(grid[i][j] == 1) {
                    x.push_back(j);
                    y.push_back(i);
                }
            }
        }
        
        //find median
        sort(x.begin(),x.end());
        sort(y.begin(),y.end());
        int num = x.size();
        int mx = x[num/2];
        int my = y[num/2];
        
        //calculate distance
        int res = 0;
        for(int i = 0; i < num; i++) {
            int d = abs(x[i] - mx) + abs(y[i] - my);
            res += d;
        }
        return res;
    }
};