number-of-islands.py

class Solution:
    def numIslands(self, grid: List[List[str]]) -> int:
        if not grid : return 0
        res = 0
        
        def dfs(i, j):
            grid[i][j] = '2'
            if i > 0 and grid[i - 1][j] == '1':
                dfs(i - 1, j)
            if i < len(grid) - 1 and grid[i + 1][j] == '1':
                dfs(i + 1, j)
            if j > 0 and grid [i][j - 1] == '1':
                dfs(i, j - 1)
            if j < len(grid[0]) - 1 and grid[i][j + 1] == '1':
                dfs(i, j + 1)
        
        for i in range(len(grid)):
            for j in range(len(grid[0])):
                if grid[i][j] == '1':
                    dfs(i, j)
                    res += 1
        return res