Pacific Atlantic Water Flow

Understand and solve the interview question "Pacific Atlantic Water Flow".


There is an m x n rectangular island that borders both the Pacific and the Atlantic oceans. The island is partitioned into a grid of square cells.

The island receives a lot of rain, and the rainwater 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.

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), we need to return a 2D list of grid coordinates result where result[i] = [ri, ci] denotes that rainwater can flow from cell (ri, ci) to both the Pacific and Atlantic oceans.

The Pacific Ocean touches the island’s left and top edges, and the Atlantic Ocean touches the island’s right and bottom edges.

Let’s review an example below:

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