Pacific Atlantic Water Flow

Medium~30 min

There is an m x n rectangular island that borders both the Pacific Ocean and the 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).

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 [r, c] where rain water can flow to both the Pacific and Atlantic oceans.

Examples

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: These 7 cells can flow water to both oceans. For example, (2,2) with height 5 can flow left/up to the Pacific and right/down to the Atlantic.
Example 2
Input: heights = [[1]]
Output: [[0, 0]]
Explanation: The single cell borders both oceans.

Constraints

  • m == heights.length
  • n == heights[r].length
  • 1 <= m, n <= 200
  • 0 <= heights[r][c] <= 100000
  • Expected time complexity: O(m × n)
Code
Ctrl+EnterRun|Ctrl+⇧+EnterSubmit
Output

Run your code to see results

Use Cmd+Enter to run