leetcode 200. Number of Islands

class Solution(object):    def dfs(self,grid,i,j):        if i < 0 or j < 0 or i >= len(grid) or j >= len(grid[0]) or grid[i][j] == '0':            return        grid[i][j] = '0'        self.dfs(grid,i+1,j)        self.dfs(grid,i,j+1)        self.dfs(grid,i-1,j)        self.dfs(grid,i,j-1)            def numIslands(self, grid):        """        :type grid: List[List[str]]        :rtype: int        """        count = 0        for i in range(len(grid)):            for j in range(len(grid[0])):                if grid[i][j] == '1':                    count += 1                    self.dfs(grid,i,j)        return count