947. Most Stones Removed with Same Row or Column

Posted 2021-02-04 tobeabetterpig

On a 2D plane, we place stones at some integer coordinate points.  Each coordinate point may have at most one stone.

Now, a move consists of removing a stone that shares a column or row with another stone on the grid.

What is the largest possible number of moves we can make?

 

Example 1:

Input: stones = [[0,0],[0,1],[1,0],[1,2],[2,1],[2,2]]
Output: 5

Example 2:

Input: stones = [[0,0],[0,2],[1,1],[2,0],[2,2]]
Output: 3

Example 3:

Input: stones = [[0,0]]
Output: 0

class Solution {
    public int removeStones(int[][] stones) {
        if(stones == null || stones.length <= 1) return 0;
        int n = stones.length;
        int[] p = new int[n];
        for(int i = 0; i < n; i++) p[i] = -1;
        for(int i = 0; i < n; i++){
            for(int j = i + 1; j < n; j++){
                if(stones[i][0] == stones[j][0] || stones[i][1] == stones[j][1]){
                    union(p, i, j);
                }
            }
        }
        for(int e : p){
            if(e == -1){
                n--;
            }
        }
        return n;
    }
    private void union(int[] p, int i, int j){
        int rooti = find(p, i);
        int rootj = find(p, j);
        if(rooti != rootj){
            p[rooti] = rootj;
        }
    }
    
    private int find(int[] p, int i){
        if(p[i] == -1) return i;
        return find(p, p[i]);
    }
}