130_SurroundedArea.txt

class Solution {
public:
    void solve(vector<vector<char>>& board) {
        if(board.size()==0)
            return;
        int m = board.size();
        int n = board[0].size();
        for(int i = 0;i<m;i++){
            for(int j = 0;j < n;j++){
                //判断是否在边界,边界上的'O'都不会被填充为'X'
                bool flag = (i==0 || j==0 || i==m-1 || j==n-1);
                if(flag && board[i][j]=='O' )
                    my_dfs(board,i,j);//找到所有与边界上的‘O’相连的‘O’
            }
        }
        for(int i = 0;i<m;i++){
            for(int j = 0;j < n;j++){
                //如果不与边界'O'相连则需要被'X'填充
                if(board[i][j] == 'O')
                    board[i][j] = 'X';
                //否则还原为'O'
                else if(board[i][j] == '#')
                    board[i][j] = 'O';
            }
        }
    }
    void my_dfs(vector<vector<char>>& board,int i,int j){
        if(i >= 0 && i<board.size() && j >= 0 && j<board[0].size() && board[i][j] == 'O'){
            board[i][j] = '#';//将所有与边界上的‘O’相连的‘O’改为‘#’便于之后的操作
            my_dfs(board,i-1,j);//上
            my_dfs(board,i+1,j);//下
            my_dfs(board,i,j-1);//左
            my_dfs(board,i,j+1);//右
        }
    }
};