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What is the overall time complexity of this approach in terms of n, the number of nodes?

medium💡 Conceptual Thinking Q5 of Q15
Tree: Depth-First Search - Diameter of Binary Tree
In the naive recursive approach to find the diameter of a binary tree, the height of each subtree is recalculated multiple times. What is the overall time complexity of this approach in terms of n, the number of nodes?
AO(n<sup>2</sup>)
BO(n log n)
CO(n)
DO(log n)
Step-by-Step Solution
Solution:
  1. Step 1: Understand the naive approach

    For each node, the algorithm computes the height of its left and right subtrees separately.
  2. Step 2: Analyze height computation cost

    Computing height for a subtree rooted at a node takes O(n) in the worst case.
  3. Step 3: Total cost

    Since height is computed for every node, total time is O(n) * O(n) = O(n2).
  4. Final Answer:

    Option A -> Option A
  5. Quick Check:

    Repeated height calculations cause quadratic time [OK]
Quick Trick: Repeated height calls cause O(n^2) time complexity [OK]
Common Mistakes:
MISTAKES
  • Assuming height calculation is O(1)
  • Confusing with optimized O(n) approach
  • Ignoring repeated subtree height computations
Trap Explanation:
PITFALL
  • Thinking height calculation is constant time leads to underestimating complexity.
Interviewer Note:
CONTEXT
  • Tests understanding of recursive complexity and inefficiencies in naive tree algorithms.
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