leetcode: surrounded-regions

if(board.size()<=2||board[0].size()<=2) return; 这句代码不写感觉也不影响整个算法呀，但是没有这句话就会报堆栈溢出错误。
还有就是将 row 和 col 定义为类的变量时也会报堆栈溢出错误。
但是在VS上没有这两句也可以正常运行，感觉很蒙，请大神指点。

class Solution {
    const int dir[4][2] = { -1,0,1,0,0,1,0,-1 };
    public:
    void solve(vector<vector<char>> &board)
    {
        int row = board.size();  // 1
        int col = board[0].size(); //2
        if(board.size()<=2||board[0].size()<=2) return;  //3
        for (int i = 0;i<row;i++)
        {
            if (board[i][0] == 'O')
                dfs(i, 0, board);
            if (board[i][col - 1] == 'O')
                dfs(i, col - 1, board);
        }
        for (int j = 0;j<col;j++)
        {
            if (board[0][j] == 'O')
                dfs(0, j, board);
            if (board[row - 1][j] == 'O')
                dfs(row - 1, j, board);
        }
        for (int i = 0;i<row;i++)
            for (int j = 0;j<col;j++)
            {
                if (board[i][j] == 'O')
                    board[i][j] = 'X';
                else if (board[i][j] == 'a')
                    board[i][j] = 'O';
            }
    }
    void dfs(int i, int j, vector<vector<char>> &board)
    {
        int row = board.size();
        int col = board[0].size();
        board[i][j] = 'a';
        for (int k = 0;k<4;k++)
        {
            int x = i + dir[k][0];
            int y = j + dir[k][1];
            if (x >= 0 && x<row&&y >= 0 && y<col)
                if (board[x][y] == 'O')
                    dfs(x, y, board);
        }
    }
};