题目：
题解：
class Solution:def dfs(self, grid, r, c):grid[r][c] = 0nr, nc = len(grid), len(grid[0])for x, y in [(r - 1, c), (r + 1, c), (r, c - 1), (r, c + 1)]:if 0 <= x < nr and 0 <= y < nc and grid[x][y] == "1":self.dfs(grid, x, y)def numIslands(self, grid: List[List[str]]) -> int:nr = len(grid)if nr == 0:return 0nc = len(grid[0])num_islands = 0for r in range(nr):for c in range(nc):if grid[r][c] == "1":num_islands += 1self.dfs(grid, r, c)return num_islands
