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