# Leetcode 1254. Number of closed islands

## DFS

class Solution:
    def closedIsland(self, grid: List[List[int]]) -> int:
        output = 0
        directional_map = [[-1,0],[0,-1],[1,0],[0,1]]
        rows = len(grid)
        cols = len(grid[0])

        def dfs(node: int):
            x = node // cols
            y = node % cols

            if grid[x][y] == 1 or grid[x][y] == -1:
                return True

            grid[x][y] = -1
            res = True
            for _x,_y in directional_map:
                new_x = x + _x
                new_y = y + _y
                if new_x < 0 or new_y < 0 or new_x >= rows or new_y >= cols:
                    res = False
                    continue
                if not dfs(new_x * cols + new_y):
                    res = False
            return res

        for node in range(rows * cols):
            x = node // cols
            y = node % cols
            if grid[x][y] == 0 and dfs(node):
                output += 1
        
        return output