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

首先判断“边框”两行两列的O，并深度遍历与其邻接的点O，将其都设为一个*标志；

然后将所有的O设为X，最后将设为*标志的恢复成X。

class Solution {
public:
    void solve(vector<vector<char>> &board) {
        int row = board.size();
        int col = board[0].size();
        if(row <= 2 || col <= 2)  return;
        for(int i = 0; i < row; i++){
            for(int j = 0; j < col; j++){
                if((board[i][j] == 'O' && i == 0) || (board[i][j] == 'O' && i == row - 1))
                    dfs(board, i, j);
                else if((board[i][j] == 'O' && j == 0) || (board[i][j] == 'O' && j == col - 1))
                    dfs(board, i, j);
            }
        }
        getResult(board);
    }
private:
    void dfs(vector<vector<char>> &board, int Row, int Col){
        if(board[Row][Col] == 'O'){
            board[Row][Col] = '*';
            if(Row - 1 >= 0)
                dfs(board, Row - 1, Col);
            if(Row + 1 <= board.size()-1)
                dfs(board, Row + 1, Col);
            if(Col - 1 >= 0)
                dfs(board, Row, Col - 1);
            if(Col + 1 < board[0].size())
                dfs(board, Row, Col + 1);
        }
        else
            return;
    }
    void getResult(vector<vector<char>> &board){
        for(int row = 0; row < board.size(); row++)
            for(int col = 0; col < board[0].size(); col++){
                if(board[row][col] == '*')
                    board[row][col] = 'O';
                else if(board[row][col] == 'O')
                    board[row][col] = 'X';
            }
    }
};