Section checkpoint

Next Level (Brief)

8 questions drawn from the 4 chapters in this section. If most land on the first try, you are ready for the next section. If not, the explanation after each answer says which idea to revisit.

Checkpoint

8 questions · first-try answers earn the most XP

1. How do you find the minimum number of meeting rooms?

2. What is the total complexity of merging intervals?

3. For a "clone graph" problem, why does DFS suit it better than BFS?

4. When should you prefer DFS over BFS in a graph problem?

5. In house robber, what does the `max(dp[i-1], dp[i-2] + nums[i])` choice represent?

6. Why is bottom-up usually preferred over recursion with memoisation in interviews?

7. How is rotting oranges related to the shortest-path family?

8. Why is it safe to mark a matrix cell as 2 to avoid revisiting it in BFS?

What this checkpoint covers

Intervals
Merge, insert — sort by start.
Graphs: BFS/DFS
Islands, clone graph idea.
DP for Beginners
Climb stairs → house robber, memo vs tab.
Matrix BFS: Rotting Oranges
Multi-source BFS levels = minutes.

Next section: Mock & Strategy