Leetcode 417. Pacific Atlantic Water Flow
Given an m×n height grid where water can flow from a cell to any neighbor of lesser-or-equal height, return all coordinates from which water can reach both the Pacific (top/left edges) and Atlantic (bottom/right edges). The core challenge is a graph/grid reachability problem typically solved by two multi-source traversals (BFS/DFS) from the ocean borders, propagating uphill (to equal-or-higher heights) and intersecting the reachable sets.
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Amazon
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Mid November, 2025
Amazon
Mid-level
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.
Early April, 2025
Merge
Senior
Late November, 2024
Meta
Junior
Solve a variation of Pacific Atlantic Water Flow without oceans
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