130.cpp

#include<iostream>
#include<cstdio>
#include<cmath>
#include<string>
#include<cstring>
#include<algorithm>
#include<vector>
#include<set>
#include<map>
#include<bitset>
using namespace std;

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