1254. Number of Closed Islands

https://leetcode.com/problems/number-of-closed-islands

Python

DFS

class Solution:
    def closedIsland(self, grid: List[List[int]]) -> int:
        m, n = len(grid), len(grid[0])

        # 0: Not visited island block
        # 1: Water
        # 2: Visited island block
        def dfs(i: int, j: int) -> bool:
            if i < 0 or j < 0 or i >= m or j >= n:
                return True

            if grid[i][j] > 0:
                return False

            grid[i][j] = 2

            return any([
                dfs(i+rx, j+cx)
                for rx, cx
                in [(-1, 0), (1, 0), (0, -1), (0, 1)]
            ])

        ans = 0
        for i in range(m):
            for j in range(n):
                if grid[i][j] == 0 and not dfs(i, j):
                    ans += 1

        return ans