LEETCODE 200. 岛屿数量

class Solution:
    def dfs(self,grid: List[List[str]],i:int,j:int):
        if grid[i][j]=='1':
            grid[i][j]='0'
        else:
            return
        if i>0:
            self.dfs(grid,i-1,j)
        if i<len(grid)-1:
            self.dfs(grid,i+1,j)
        if j>0:
            self.dfs(grid,i,j-1)
        if j<len(grid[0])-1:
            self.dfs(grid,i,j+1)
            

    def numIslands(self, grid: List[List[str]]) -> int:
        # dfs
        res=0
        for i in range(len(grid)):
            for j in range(len(grid[0])):
                if grid[i][j]=='1':
                    self.dfs(grid, i, j)
                    res+=1
        return res