LeetCode-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

public class Solution {
    public void solve(char[][] board) {
        if(board == null || board.length < 2 || board[0].length < 2){
            return;
        }
        int row = board.length;
        int col = board[0].length;
        for(int i = 0; i < row; i++){
            if(board[i][0] == 'O'){
                 
                check(board, i, 0);
            }
            if(board[i][col - 1] == 'O'){
                check(board, i, col - 1);
            }
        }
        for(int i = 0; i < col; i++){
            if(board[0][i] == 'O'){
                check(board, 0, i);
            }
            if(board[row - 1][i] == 'O'){
                check(board, row - 1, i);
            }
        }
        for(int i = 0; i < row; i++){
            for(int j = 0; j < col; j++){
                if(board[i][j] == 'O'){
                    board[i][j] = 'X';
                }
                if(board[i][j] == 'C'){
                    board[i][j] = 'O';
                }
            }
        }
    }
     
    public void check(char[][] board, int i, int j){
       if(i < 0 || i >= board.length || j < 0 || j >= board[0].length){
           return;
       }
       if(board[i][j] == 'O'){
           board[i][j] = 'C';
       }
       if(j < board[0].length - 2 && board[i][j + 1] == 'O'){
           check(board, i , j + 1);
       }
       if(j > 1 && board[i][j - 1] == 'O'){
            check(board, i , j - 1);
       }
       if(i < board.length - 2 && board[i + 1][j] == 'O'){
            check(board, i + 1 , j);
       }
       if(i > 1 && board[i - 1][j] =='O'){
            check(board, i - 1, j);
       }
    }
}