Number of Islands

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

        def dfs(r: int, c: int) -> None:
            if (
                r < 0
                or r >= rows
                or c < 0
                or c >= cols
                or grid[r][c] != "1"
            ):
                return
            grid[r][c] = "0"
            dfs(r + 1, c)
            dfs(r - 1, c)
            dfs(r, c + 1)
            dfs(r, c - 1)

        for r in range(rows):
            for c in range(cols):
                if grid[r][c] == "1":
                    count += 1
                    dfs(r, c)
        return count