python 学习 leetcode ---number of island

class Solution(object):
    def numIslands(self, grid):
        """
        :type grid: List[List[str]]
        :rtype: int
        """
        count=0
        m=len(grid)
        if m==0:
            return  0
        n=len(grid[0])
        #visit=[[False]*n]*m
        visit = [[False for i in range(n)]for j in range(m)]  
        def check(x, y):  
            if x >= 0 and x<m and y>= 0 and y< n and grid[x][y] == ‘1‘ and visit[x][y] == False:  
                return True  
        def dfs(i ,j):
            nbrow = [1,0,-1,0]  
            nbcol = [0,1,0,-1] 
            for d in range(4):
                ni=i+nbrow[d]
                nj=j+nbcol[d]
                if(check(ni,nj)==True):
                    visit[ni][nj]=True
                    dfs(ni,nj)
        for i in range(m):
            for j in range(n):
                if(check(i,j)==True):
                    visit[i][j]=True
                    dfs(i,j)
                    count+=1
        return count