Please solve the programming task below using a self-contained code snippet in a markdown code block.

Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water), return 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.
 
Please complete the following python code precisely:
```python
class Solution:
    def numIslands(self, grid: List[List[str]]) -> int:
        
```