Number of Islands

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

        rows, cols = len(grid), len(grid[0])
        visit = set()
        count = 0

        def dfs(r, c):
            if r in range(rows) and c in range(cols) and (r,c) not in visit and grid[r][c] == "1":
                visit.add((r,c))
                for dr, dc in [[0, 1], [1, 0], [-1, 0], [0, -1]]:
                    dfs(r+dr, c+dc)

        for r in range(rows):
            for c in range(cols):
                if grid[r][c] == "1" and (r,c) not in visit:
                    count += 1
                    dfs(r,c)
        
        return count