LeetCode #200 - Number of Islands\nGiven a 2D grid 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.\n\n### Problem Statement\n```python\ndef num_islands(grid: List[List[str]]) -> int:\n```\n### Example 1\n**Input:** ["11110", "11010", "11000", "00000"] \n**Output:** 1 \n**Explanation:** There is one island.\n\n### Example 2\n**Input:** ["11000", "11000", "00100", "00011"] \n**Output:** 3 \n**Explanation:** There are three islands.\n\n### Constraints\n* 1 <= grid.length, grid[0].length <= 300\n* grid[i][j] is '0' or '1'.