Surrounded Regions

Surrounded Regions

Given a 2D board containing 'X' and 'O', capture all regions surrounded by 'X'.

A region is captured by flipping all 'O's into 'X's in that surrounded region.

For example,

X X X X
X O O X
X X O X
X O X X

After running your function, the board should be:

X X X X
X X X X
X X X X
X O X X

Java代码：

public class Solution {  
    private int m, n;  
    private char[][] board;  
    private Queue<Integer> queue = new LinkedList<Integer>();  
  
    public void add(int x, int y) {  
        if (x >= 0 && x < m && y >= 0 && y < n && board[x][y] == 'O') {  
            board[x][y] = 'Z';  
            queue.offer(x * n + y);  
        }  
    }  
      
    public void traversal(int x, int y) {  
        add(x, y);  
        while (!queue.isEmpty()) {  
            int p = queue.poll();  
            int px = p / n;  
            int py = p % n;  
            add(px - 1, py);  
            add(px + 1, py);  
            add(px, py - 1);  
            add(px, py + 1);  
        }  
    }  
  
    public void solve(char[][] board) {  
        // Start typing your Java solution below  
        // DO NOT write main() function  
        if (board == null || board.length == 0 || board[0].length == 0) {  
            return;  
        }  
        this.board = board;  
        m = board.length;  
        n = board[0].length;          
        for (int i = 0; i < n; i++) {  
            traversal(0, i);  
            traversal(m - 1, i);              
        }  
        for (int i = 0; i < m; i++) {  
            traversal(i, 0);  
            traversal(i, n - 1);  
        }  
        for (int i = 0; i < m; i++) {  
            for (int j = 0; j < n; j++) {  
                board[i][j] = board[i][j] == 'Z' ? 'O' : 'X';  
            }  
        }  
    }  
}