Solve the Medium-level Pacific Atlantic Water Flow coding interview problem online in Python & JavaScript. Run your code against real test cases in the browser and study worked examples. It covers graph, matrix, depth first search, and breadth first search. Read the step-by-step solution and complexity analysis. Java starter code is also included for reference (no in-browser JVM yet, so it can't be run here).

Pacific Atlantic Water Flow – Solve Online in Python & JavaScript

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Clone Graph

Find grid cells that can flow to both oceans under height constraints.

Water flows from a cell to equal-or-lower neighbors. Return all `[row, column]` cells that can reach both the Pacific (top/left) and Atlantic (bottom/right), in row-major order.

## Example
```json
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]]
```

## Constraints
- 1 <= rows, columns <= 200
- 0 <= heights[r][c] <= 100000

## Follow-up
Why is reverse traversal from each ocean more efficient than searching from every cell?

The key pattern is: Reverse graph searches grow inward from both oceans. Identify the state and invariant before coding.

Recognize the Pattern

Advance one state transition at a time. Mark or update state before exploring dependent work.

Build the Algorithm

Test empty or minimal input, skewed shapes, duplicates where allowed, and impossible outcomes.