// Pacific Atlantic Water Flow — MEDIUM

// Category: graph

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.

Water can only flow in four directions (up, down, left, right) from a cell to an adjacent one with height **less than or equal** to the current cell's height.

Return a 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: 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]]