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.

样例

X X X X
X O O X
X X O X
X O X X

After capture all regions surrounded by 'X', the board should be:

X X X X
X X X X
X X X X
X O X X

class Solution {
public:
    /**
     * @param board a 2D board containing 'X' and 'O'
     * @return void
     */
    void surroundedRegions(vector<vector<char>>& board) {
        // Write your code here
        int m = board.size();
	    if (m < 1)
	    {
		    return;
	    }
	    int n = board[0].size();
	    if (n < 1)
	    {
		    return;
	    }

	    for (int i = 0; i < n; i++)
	    {
		    visit(board, m, n, 0, i);
	    }
	    for (int i = 1; i < m-1; i++)
	    {
		    visit(board, m, n, i, 0);
	    }
	    for (int i = 1; i < m-1; i++)
	    {
		    visit(board, m, n, i, n-1);
	    }
	    for (int i = 0; i < n; i++)
	    {
		    visit(board, m, n, m-1, i);
	    }

	    for (int i = 0; i < m; i++)
	    {
		    for (int j = 0; j < n; j++)
		    {
			    if (board[i][j] == 'O')
			    {
				    board[i][j] = 'X';
			    }
		    }
	    }

	    for (int i = 0; i < m; i++)
	    {
		    for (int j = 0; j < n; j++)
		    {
			    if (board[i][j] == '1')
			    {
				    board[i][j] = 'O';
			    }
		    }
	    }
    }
private:
    void visit(vector<vector<char> > &board, int m, int n, int row, int column)
    {
	    if (row < 0 || row >= m)
	    {
		    return;
	    }
	    if (column < 0 || column >= n)
	    {
		    return;
	    }
	    if (board[row][column] != 'O')
	    {
		    return;
	    }

	    board[row][column] = '1';
	    visit(board, m, n, row-1, column);
	    visit(board, m, n, row+1, column);
	    visit(board, m, n, row, column-1);
	    visit(board, m, n, row, column+1);
    }
};