How do you find cells that can flow to both Pacific and Atlantic oceans?
PICTURE THIS: HOW TO EXPLAIN IT
Simple meaning
Reverse the thinking: BFS/DFS from Pacific border cells and from Atlantic border cells uphill, then intersect the two reachable sets.
WHY — Graphs instead of guessing?
Why interviewers care about Graphs:
question about Graphs.
trade-offs, and what you would actually do on a DSA project - not buzzwords.
Name the idea, why it exists, then one short example.
End with when you use it and one common pitfall.
STEPS — What happens step by step?
Before you speak the answer, walk the interviewer through these steps:
- 1Reverse the thinking: BFS/DFS
from Pacific border cells and from Atlantic border cells uphill, then intersect the two reachable sets.
- 2Time is O(m*n) and
space is O(m*n).
- 3Starting from every cell
toward oceans would be much slower.
- 4Give an example
One tiny concrete case you can say aloud.
- 5Common mistake
What juniors usually get wrong.
- 6Close
When you pick this over the alternative.
EXAMPLE — See it in action
Here's a short line you can speak, broken into clear beats:
Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.
Key takeaway
Reverse the thinking: BFS/DFS from Pacific border cells and from Atlantic border cells uphill, then intersect the two reachable sets. Time is O(m*n) and space is O(m*n).