number.py

from typing import List

class Solution:
    def numIslands(self, grid: List[List[str]]) -> int:
        if not grid or not grid[0]:
            return 0
            
        rows, cols = len(grid), len(grid[0])
        count = 0

        def dfs(r, c):
            if r < 0 or r >= rows or c < 0 or c >= cols or grid[r][c] != '1':
                return
            grid[r][c] = '#'  # Mark the cell as visited
            # Explore all four possible directions
            dfs(r + 1, c)
            dfs(r - 1, c)
            dfs(r, c + 1)
            dfs(r, c - 1)

        for i in range(rows):
            for j in range(cols):
                if grid[i][j] == '1':  # Found an unvisited land
                    dfs(i, j)  # Start DFS from here
                    count += 1  # Increase island count

        return count