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g0401_0500.s0417_pacific_atlantic_water_flow.readme.md Maven / Gradle / Ivy

417\. Pacific Atlantic Water Flow

Medium

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:**

![](https://assets.leetcode.com/uploads/2021/06/08/waterflow-grid.jpg)

**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