假設有一個棋盤(二維座標系), 棋盤上擺放了一些石子(每個石子的座標都為整數). 你可以remove一個石子, 當且僅當這個石子的同行或者同列還有其它石子. 輸入是一個list of points.

問:
1) 給這些石子座標, 你最多能remove多少個石子?
2) Follow-up: 若想保證remove的石子數量最大, 應按照什麼順序remove? (沒有寫程式碼)

DFS count connected components:

// "static void main" must be defined in a public class.
public class
 
 Main {
    public static void main(String[] args) {
        int[] a = {0,0};
        int[] b = {0,1};
        int[] c = {1,2};
        int[] d = {2,3};
        List<int[]> coords = new ArrayList<>();
        coords.add(a);
        coords.add(b);
        coords.add(c);
        coords.add(d);
        
        System.out.println(
 
new Solution().minReminingChessPieces(coords));
    }
}
class Solution{
    
    public int minReminingChessPieces(List<int[]> coords){
        if(coords == null){
            return -1;
        }
        HashSet<String> visited = new HashSet<>();
        int res = 0;
        for(int
 
[] coord : coords){
            String s = coord[0]+":"+coord[1];
            if(!visited.contains(s)){
                res++;
                DFSHelper(coords, coord, visited);
            }
        }
        return res;
    } 
    
    public void DFSHelper(List<int[]> coords, int[] coord, HashSet<String> visited){
        visited.add(coord[0]+":"+coord[1]);
        for(int[] subCoord : coords){
            if(subCoord[0] == coord[0] || subCoord[1] == coord[1]){
                if(!visited.contains(subCoord[0]+":"+subCoord[1])){
                    DFSHelper(coords, subCoord, visited);
                }
            }
        }
    }
    
}