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

        def dfs(r, c):

            if r<0 or r>=len(grid) or c<0 or c>=len(grid[0]) or grid[r][c]=="0":
                return

            grid[r][c] = "0"

            dfs(r+1, c)
            dfs(r-1, c)
            dfs(r, c+1)
            dfs(r, c-1)

            return

        count = 0
        for r in range(len(grid)):
            for c in range(len(grid[0])):
                if grid[r][c] == "1":
                    dfs(r, c)
                    count = count+1

        return count