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Surrounded Region

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Linkage

https://leetcode.com/problems/surrounded-regions/description/

Code

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class Solution {
    public void solve(char[][] board) {
        int row_number = board.length;
        if (row_number == 0) return;
        int col_number = board[0].length;
        
        for (int i = 0; i < row_number; i++){
            search(board, i, 0);
            search(board, i, col_number - 1);
        }
        
        for (int j = 0; j < col_number; j++){
            search(board, 0, j);
            search(board, row_number - 1, j);
        }
        
        for (int i = 0; i < row_number; i++){
            for(int j = 0; j < col_number; j++){
                if(board[i][j] != 'M')
                    board[i][j] = 'X';
                else
                    board[i][j] = 'O';
            }
        }
    }
    
    public void search(char[][] board, int i, int j) {
        int row_number = board.length;
        int col_number = board[0].length;
        if (i < 0 || i >= row_number || j < 0 || j >= col_number || board[i][j] != 'O')
            return;
        
        board[i][j] = 'M';
        
        int[][] directions = {{-1, 0}, {1, 0}, {0, -1}, {0, 1}}; 
        for(int direction = 0; direction < 4; direction++){
            int row = i + directions[direction][0];
            int col = j + directions[direction][1];
            search(board, row, col);
        }
        return;
    }
    
}