You are given an m x n integer matrix heights representing the height of each unit cell in a continent. The Pacific ocean touches the continent's left and top edges, and the Atlantic ocean touches the continent's right and bottom edges.
Water can only flow in four directions: up, down, left, and right. Water flows from a cell to an adjacent one with an equal or lower height.
Return a list of grid coordinates where water can flow 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]]
Example 2:
Input: heights = [[2,1],[1,2]] Output: [[0,0],[0,1],[1,0],[1,1]]
Constraints:
m == heights.lengthn == heights[i].length1 <= m, n <= 2001 <= heights[i][j] <= 105