200. Number-of-Island

class Solution:
    def numIslands(self, grid: List[List[str]]) -> int:
        m = len(grid)
        n = len(grid[0])
        dir = [0,1,0,-1,0]
        res = 0

        def dfs(row, col):
            if row < 0 or row == m or col < 0 or col == n or grid[row][col] == '0':
                return
            grid[row][col] = '0'
            for i in range(4):
                dfs(row + dir[i],col + dir[i+1])

        for i in range(m):
            for j in range(n):
                if grid[i][j] == '1':
                    res += 1
                    dfs(i,j)
        
        return res