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';

        }

    }

}

};