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You are given two arrays representing the inorder and postorder traversal sequences of a binary tree. Which approach guarantees reconstructing the original tree efficiently without redundant searches?

easy🔍 Pattern Recognition Q11 of Q15
Tree: Depth-First Search - Construct Tree from Inorder and Postorder
You are given two arrays representing the inorder and postorder traversal sequences of a binary tree. Which approach guarantees reconstructing the original tree efficiently without redundant searches?
AUse a greedy approach by always attaching nodes as left children when possible.
BUse dynamic programming to store subtrees and avoid recomputation.
CUse recursion with a hash map to quickly find root indices in the inorder array.
DUse breadth-first search to reconstruct the tree level by level.
Step-by-Step Solution

  1. Step 1: Understand the problem constraints

    Reconstructing a tree from inorder and postorder requires identifying root nodes and splitting subtrees efficiently.

  2. Step 2: Evaluate approaches

    Recursion with a hash map allows O(1) root index lookup in inorder, avoiding repeated linear searches and ensuring O(n) time.

  3. Final Answer:

    Option C -> Option C

  4. Quick Check:

    Hash map lookup avoids O(n) search per recursion [OK]
Quick Trick: Hash map lookup avoids repeated linear searches [OK]
Common Mistakes:
MISTAKES
  • Assuming greedy or BFS can reconstruct tree uniquely
  • Confusing DP with tree construction
  • Ignoring index lookup cost
Trap Explanation:
PITFALL
  • Greedy or BFS approaches seem intuitive but fail to handle subtree splits correctly; DP is unrelated here.
Interviewer Note:
CONTEXT
  • Tests if candidate recognizes the optimal pattern beyond brute force or naive methods.
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