AlgoSolveoRoadmap › Stage 6: Trees › Pattern 29 of 53
DSA pattern guide
Tree — LCA & Construction
Lowest common ancestor, build a tree from traversals, serialize.
Use it when
Lowest common ancestor, build a tree from traversals, serialize.
Key idea
LCA: the node where p and q split into different subtrees. Construction: the preorder root splits the inorder array.
Practice problems, in order
- Invert Binary TreeEasy
- Lowest Common Ancestor of Binary TreeMedium
- Flatten Binary Tree to Linked ListMedium
- Construct Binary Tree from Preorder & InorderMedium
- Construct Binary Tree from Inorder & PostorderMedium
- Kth Ancestor of a Tree NodeHard
- Serialize and Deserialize Binary TreeHard
How to practise this pattern
- Read the problem and look for the signal above before writing any code.
- Say the brute force out loud, with its time complexity, then ask what work it repeats.
- Apply the key idea and write the optimised version yourself.
- If you're stuck for more than 10 minutes, take one small hint, not the full solution.
- Move to the next problem only when you can explain why this pattern fits.
Stuck on one of these?
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