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

Difficulty: interview

Starter code:

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

Solutions:
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