LC_130

class Solution {

    public void solve(char[][] board) {

        int rows = board.length;
        int cols = board[0].length;


        for(int i = 0; i < rows; i++){
            if(board[i][0] == 'O')
                dfs(board, i, 0);
        }
        for(int i = 0; i < rows; i++){
            if(board[i][cols - 1] == 'O')
                dfs(board, i, cols - 1);
        }

        for(int j = 0; j < cols; j++){
            if(board[0][j] == 'O')
                dfs(board, 0, j);
        }
        for(int j = 0; j < cols; j++){
            if(board[rows - 1][j] == 'O')
                dfs(board, rows - 1, j);
        }
        for(int i = 0; i < rows; i++){
            for(int j = 0; j < cols; j++){

                if(board[i][j] == 'O')
                    board[i][j] = 'X';

                else if(board[i][j] == 'S')
                    board[i][j] = 'O';
            }
        }
    }

    private void dfs(char[][] board, int row, int col){

        if(row < 0 ||
           row >= board.length ||
           col < 0 ||
           col >= board[0].length ||
           board[row][col] != 'O')
            return;

        board[row][col] = 'S';

        dfs(board,row+1,col);
        dfs(board,row-1,col);
        dfs(board,row,col+1);
        dfs(board,row,col-1);
    }
}