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. The island is partitioned into a grid of square cells. You are given an `m x n` integer matrix `heights` where `heights[r][c]` represents the **height above sea level** of the cell at coordinate `(r, c)`. The island receives a lot of rain, and the rain water can flow to neighboring cells directly north, south, east, and west if the neighboring cell's height is **less than or equal to** the current cell's height. Water can flow from any cell adjacent to an ocean into the ocean. Return _a **2D list** of grid coordinates _`result`_ where _`result[i] = [ri, ci]`_ denotes that rain water can flow from cell _`(ri, ci)`_ to **both** the Pacific and Atlantic oceans_.   **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] <= 105`