human
What is a the Python code you requested given the following:
I found an interesting problem on https://leetcode.com/problems/number-of-islands/:
Given a 2d grid map of '1's (land) and '0's (water), count the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water.

Example 1:

Input:
11110
11010
11000
00000

Output: 1

Example 2:

Input:
11000
11000
00100
00011

Output: 3

I tried it in Python, but could not do it. Can you solve it?
assistant
#Here is the Python code you requested.

class Solution:
     def expandIsland(self, grid, i, j):
         edges = [(i, j)]
         while edges:
             next_edges = []
             for edge in edges:
                 ei, ej = edge
                 if ei >= 0 and ei < len(grid) and ej >= 0 and ej < len(grid[ei]) and grid[ei][ej] == '1':
                     grid[ei][ej] = '2'
                     next_edges.append((ei + 1, ej))
                     next_edges.append((ei, ej + 1))
                     next_edges.append((ei - 1, ej))
                     next_edges.append((ei, ej - 1))
             edges = next_edges
     
     def numIslands(self, grid):
         """
         :type grid: List[List[str]]
         :rtype: int
         """
         island_count = 0
         for i in range(len(grid)):
             for j in range(len(grid[i])):
                 if grid[i][j] == '1':
                     island_count += 1
                     self.expandIsland(grid, i, j)
         return island_count