Surrounded Regions

 1 import java.util.LinkedList;
 2 import java.util.Queue;
 3 
 4 public class Solution {
 5     private char board[][];
 6     private int rows;
 7     private int cols;                                                        //行和列数
 8     private Queue<Integer> queue = new LinkedList<Integer>();                //BFS使用的队列
 9     
10     public void solve(char[][] board) {
11         this.board = board;
12         if(null == board || board.length == 0 || board[0].length == 0)        //特殊的直接返回
13             return;
14         rows = this.board.length;
15         cols = this.board[0].length;                                        //获取行和列的数目
16         
17         for(int i = 0; i < rows; i++){
18             traver(i, 0);                                                    //第一列
19             traver(i, cols - 1);                                            //最后一列
20         }
21         for(int i = 0; i < cols; i++){
22             traver(0, i);                                                    //第一行
23             traver(rows - 1, i);                                            //最后一行
24         }
25         //遍历整个数组
26         for(int i = 0; i < rows;i++){
27             for(int j = 0; j < cols; j++){
28                 board[i][j] = this.board[i][j] == ‘Z‘ ? ‘O‘ : ‘X‘;
29             }
30         }
31     }
32     
33     /**
34      * 对x,y所指的单元进行BFS
35      * @param x
36      * @param y
37      */
38     public void traver(int x, int y){
39         add(x, y);
40         while(!this.queue.isEmpty()){
41             int head = queue.poll();                                        //出队列
42             int temp_x = head / cols;
43             int temp_y = head % cols;
44             add(temp_x - 1, temp_y);
45             add(temp_x + 1, temp_y);
46             add(temp_x, temp_y - 1);
47             add(temp_x, temp_y + 1);                                        //flood fill算法的体现
48         }
49     }
50     
51     /**
52      * x,y所指的单元如果是‘o‘放到队列中,x * cols + y
53      * @param x
54      * @param y
55      */
56     public void add(int x, int y){
57         if(x >= 0 && x < rows && y >= 0 && y < cols && this.board[x][y] == ‘O‘)
58         {
59             this.queue.add(x * cols + y);
60             this.board[x][y] = ‘Z‘;
61         }
62     }
63     
64 }