417. Pacific Atlantic Water Flow

There is an m x n rectangular island that borders both the Pacific Ocean and Atlantic Ocean. The Pacific Ocean touches the island's left and top edges, and the Atlantic Ocean touches the island's right and bottom edges

Array

Example 1:

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.

Example 2:

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

Constraints:

m == heights.length
n == heights[r].length
1 <= m, n <= 200
0 <= heights[r][c] <= 10^5

Solution

class Solution:
    def pacificAtlantic(self, heights: list[list[int]]) -> list[list[int]]:
        rows, cols = len(heights), len(heights[0])
        pac, atl = set(), set()

        def dfs(r, c, seen, prevHeight):
            if (
                (r, c) in seen
                or r < 0
                or c < 0
                or r == rows
                or c == cols
                or heights[r][c] < prevHeight
            ):
                return
            seen.add((r, c))
            dfs(r + 1, c, seen, heights[r][c])
            dfs(r - 1, c, seen, heights[r][c])
            dfs(r, c + 1, seen, heights[r][c])
            dfs(r, c - 1, seen, heights[r][c])

        for c in range(cols):
            dfs(0, c, pac, heights[0][c])
            dfs(rows - 1, c, atl, heights[rows - 1][c])

        for r in range(rows):
            dfs(r, 0, pac, heights[r][0])
            dfs(r, cols - 1, atl, heights[r][cols - 1])

        res = []
        for r in range(rows):
            for c in range(cols):
                if (r, c) in pac and (r, c) in atl:
                    res.append([r, c])

        return res