Number of Islands

class Solution {
public:
    bool valid (int r , int c , int rows, int cols)
    {
        return ( (r >= 0 && r < rows ) && (c >= 0 && c < cols));
    }
    void dfs (vector<vector<char>>& grid, int r , int c , int rows, int cols)
    {

        if (!valid (r, c, rows, cols) || grid[r][c] == '0')
            return;
       //cout << r << c << endl;
        grid[r][c] = '0';

        dfs (grid, r + 1, c, rows, cols);
        dfs (grid, r, c + 1, rows, cols);
        dfs (grid, r - 1, c, rows, cols);
        dfs (grid, r, c - 1, rows, cols);

    }
    int numIslands(vector<vector<char>>& grid) {

        int res = 0;
        int cols = 0;
        int rows = grid.size();
        if ( rows)
        cols = grid[0].size();



        for (int r = 0 ; r < rows ; r++)
        {
            for (int c = 0 ; c < cols ; c++)
            {

                if (grid[r][c] == '1')
                {
                    res ++;

                    dfs (grid, r, c, rows, cols);

                }
            }
        }

        return res;

    }
};