【LeetCode130】被围绕的区域（dfs）

class Solution {
private:
    vector<pair<int,int>>directions{{0,1},{0,-1},{1,0},{-1,0}};
public:
    void solve(vector<vector<char>>& board) {
        int row=board.size();//row行数
        int col=board[0].size();//column列数
        for(int i=0;i<row;i++){
            for(int j=0;j<col;j++){
                if(board[i][j]=='O' && (i == row-1 || j == col-1
                   || i == 0 || j == 0)){
                    dfs(board,i,j);
                }
            }
        }
        for(int i=0;i<row;i++){
            for(int j=0;j<col;j++){
                if(board[i][j] == 'A'){
                    board[i][j] = 'O';
                }else if(board[i][j] == 'O'){
                    board[i][j] = 'X';
                }
            }
        }
    }
    void dfs(vector<vector<char>>&board,int x,int y){
        if(!isarea(board,x,y)){
            return;//如果坐标(x,y)超过网格范围，则直接返回
        }
        if(board[x][y]!='O'){
            return;//如果不是岛屿(1)则直接返回
        }
        board[x][y]='A';//将格子标记为已遍历过,重新淹水
        for(auto dir:directions){
            int newx=x+dir.first,newy=y+dir.second;
            if(isarea(board,newx,newy)){//在网格范围内(正常)
                //board[x][y]='X';
                dfs(board,newx,newy);
            }
        }
    }
    bool isarea(vector<vector<char>>&board,int x,int y){//判断点是否在网格内
        if(x>=0 && x<board.size() && 0<=y && y<board[0].size()){
            return true;
        }else{
            return false;
        }
    }  
};