LeetCode 366 | Find Leaves of Binary Tree | Solution Explained (Java + Whiteboard)

Given a binary tree, collect a tree's nodes as if you were doing this: Collect and remove all leaves, repeat until the tree is empty.
Running Time: O(N)
Space Complexity: O(N)
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[@ravinsher]

Need more white board walk through along with code.

[@pubamx]

Indeed, may be a hard concept to understand, but an easy problem if you are experienced with recursion problems. I think your solution explains itself along with the whiteboard example. Thanks for sharing.

[@jianlu9841]

I had this problem interviewed at Google back in 2021, but not binary tree, it was N-ary Tree. I was using topological sorting to resolve it.(make every node pointing to its parent node) Not at good as yours though.

[@mithileshgawande7966]

Great Job!! Very concise explanation....thank you.

[@ivaylopankov7369]

Hi Xavier, thank you for your work - keep on going! I do think though that it was worth mentioning how and way the individual levels got created in the final answer.

[@xavierelon]

Yes I try to address this but it is hard with recursion. I am still working on it

[@ivaylopankov7369]

The way I look at it is that the Tree levels are indices in the resulting list (Zero-based). The recursion execution ensures that a new index (new ArrayList) is added only the first time when a new level is discovered.

[@xavierelon]

Yes I can visualize it in my head but have trouble figuring out how to draw it out on the white board for you guys

[@vaibhavgupta973]

thank you !!

[@sundixin1146]

holy shit I think I finally understand recursion

[@xavierelon]

Haha glad you figured it out. It’s a tricky topic

[@edwardteach2]

Smart to think of it as layers and to set the not root to -1 to make the math easier to add the root values.

[@soulboy2223]

thanks, but we don't remove the leaves actually, right?

[@xavierelon]

You can if you want but it is not required. I wrote a line in a different submission that erases the leaves and it still passes all the test cases

[@xueli5641]

It helped, thanks!

[@xavierelon]

You’re welcome

[@carloscarrillo-calderon7862]

Standard optimal solution, very poor explanation...