LeetCodeAsked at 12 companies
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- Apple
- Microsoft
- Bloomberg
- Meta
- MongoDB
- X
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- General Motors
- Roblox
+2 moreShow fewer
- Nutanix
- Citadel
Community-reported · source · updated 2026-10-08. ● asked in the last 6 months.
Go step by step: try it yourself before the video and the visual. Progress saves on this device.
Step 1
Know these before you start
Tick what you already know
Concept videoStep 2
Try it on paper
5–10 minutes, no code yet
About this problem
Hierarchical nodes. Learn DFS (recursion) and BFS (queue) traversals first.
Read the full statement and examples on LeetCode, try it for 20–30 minutes, then come back for the walkthrough and the step-by-step visual.
Step 6
Get it accepted
All test cases pass
Step 7
Review it so it sticks
Re-solve from memory after
Your notes
Three lines in your own words. They come back with this problem's reviews, so you can check yourself after recalling the solution.
Solve it yourself before you look
Reading the solution first feels like progress, but it makes the next similar problem — and the interview version — much harder, because you skipped the part where you figure it out. Give it an honest 20–30 minutes. Stuck? Re-read the pattern, watch the concept video, or try the brute force first.
Hidden: optimal solution