Number of Islands

class Solution:
    def numIslands(self, grid: List[List[str]]) -> int:

        numIslands = 0

        def dfs(y, x):
            if y < 0 or y > len(grid)-1 or x < 0 or x > len(grid[y])-1:
                return

            if grid[y][x] == "1":
                grid[y][x] = "#"
                directions = [[-1, 0], [1, 0], [0, -1], [0, 1]]
                for up, down in directions:
                    dfs(y+up, x+down)

        for y in range(len(grid)):
            for x in range(len(grid[y])):
                if grid[y][x] == "1":
                    dfs(y, x)
                    numIslands += 1

        return numIslands