leetcode[130]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

class Solution {
public:
void travel(int i, int j, vector<vector<char>> &board)
{
    if(i<0||i>=board.size()||j<0||j>=board[0].size())return;
    if(board[i][j]=='O')
    {
        board[i][j]='Q';
        if(i-1>=1)travel(i-1,j,board);
        if(i+1<=board.size()-2)travel(i+1,j,board);
        if(j-1>=1)travel(i,j-1,board);
        if(j+1<=board.size()-2)travel(i,j+1,board);
    }
}
void solve(vector<vector<char>> &board)
{
    if(board.empty()||board.size()<3||board[0].size()<3)return;
    int m=board.size();
    int n=board[0].size();
    for(int i=0;i<m;i++)
    {
        if(board[i][0]=='O')travel(i,0,board);
        if(board[i][n-1]=='O')travel(i,n-1,board);
    }
    for(int j=0;j<n;j++)
    {
        if(board[0][j]=='O')travel(0,j,board);
        if(board[m-1][j]=='O')travel(m-1,j,board);
    }
    for(int i=0;i<m;i++)
    {
        for(int j=0;j<n;j++)
        {
            if(board[i][j]=='X')continue;
            board[i][j]=board[i][j]=='Q'?'O':'X';
        }
    }
}
};