class Solution:
    def islandPerimeter(self, grid: List[List[int]]) -> int:
        W = len(grid)
        H = len(grid[0])

        def is_water(x: int, y: int) -> bool:
            return not (
                0 <= x < W and
                0 <= y < H and
                grid[x][y] == 1
            )

        ans = 0
        for x in range(W):
            for y in range(H):
                if is_water(x, y):
                    continue

                for dx, dy in [(0, 1), (0, -1), (1, 0), (-1, 0)]:
                    if is_water(x + dx, y + dy):
                        ans += 1
        return ans