Pacific Atlantic Water Flow Python Solution

lcpy gen -n 417   # by problem number
lcpy gen -s pacific_atlantic_water_flow   # by problem name

Input: heights = [[1,2,2,3,5],[3,2,3,4,4],[2,4,5,3,1],[6,7,1,4,5],[5,1,1,2,4]]
Output: [[0,4],[1,3],[1,4],[2,2],[3,0],[3,1],[4,0]]
Explanation: The following cells can flow to the Pacific and Atlantic oceans, as shown below:
[0,4]: [0,4] -> Pacific Ocean
       [0,4] -> Atlantic Ocean
[1,3]: [1,3] -> [0,3] -> Pacific Ocean
       [1,3] -> [1,4] -> Atlantic Ocean
[1,4]: [1,4] -> [1,3] -> [0,3] -> Pacific Ocean
       [1,4] -> Atlantic Ocean
[2,2]: [2,2] -> [1,2] -> [0,2] -> Pacific Ocean
       [2,2] -> [2,3] -> [2,4] -> Atlantic Ocean
[3,0]: [3,0] -> Pacific Ocean
       [3,0] -> [4,0] -> Atlantic Ocean
[3,1]: [3,1] -> [3,0] -> Pacific Ocean
       [3,1] -> [4,1] -> Atlantic Ocean
[4,0]: [4,0] -> Pacific Ocean
       [4,0] -> Atlantic Ocean
Note that there are other possible paths for these cells to flow to the Pacific and Atlantic oceans.

Input: heights = [[1]]
Output: [[0,0]]
Explanation: The water can flow from the only cell to the Pacific and Atlantic oceans.

class Solution:
    # Time: O(m * n)
    # Space: O(m * n)
    def pacific_atlantic(self, heights: list[list[int]]) -> list[list[int]]:
        if not heights or not heights[0]:
            return []

        m, n = len(heights), len(heights[0])
        pacific: set[tuple[int, int]] = set()
        atlantic: set[tuple[int, int]] = set()

        def dfs(r: int, c: int, visited: set) -> None:
            visited.add((r, c))
            for dr, dc in [(0, 1), (0, -1), (1, 0), (-1, 0)]:
                nr, nc = r + dr, c + dc
                if (
                    0 <= nr < m
                    and 0 <= nc < n
                    and (nr, nc) not in visited
                    and heights[nr][nc] >= heights[r][c]
                ):
                    dfs(nr, nc, visited)

        # DFS from Pacific borders (top and left)
        for i in range(m):
            dfs(i, 0, pacific)
        for j in range(n):
            dfs(0, j, pacific)

        # DFS from Atlantic borders (bottom and right)
        for i in range(m):
            dfs(i, n - 1, atlantic)
        for j in range(n):
            dfs(m - 1, j, atlantic)

        return [[r, c] for r, c in pacific & atlantic]