Tree: Depth-First Search - Count Complete Tree Nodes
Consider the optimal countNodes function for a complete binary tree. What is the output when the input tree is empty (root = None)?
Consider the optimal countNodes function for a complete binary tree. What is the output when the input tree is empty (root = None)?
medium🧾 Code Trace Q4 of Q15
Step-by-Step Solution
Solution:
Step 1: Check base case
Input root is None, so function returns 0 immediately.Step 2: Verify return value
Function returns integer 0, not None.Final Answer:
Option C -> Option CQuick Check:
Empty tree count is 0, matching the code's return value [OK]
Quick Trick: Empty tree -> count 0 [Check carefully return type] [OK]
Common Mistakes:
MISTAKES- Assuming function returns None for empty tree
- Confusing 0 and None
Trap Explanation:
PITFALL- Candidates confuse null root with None return value, but code returns 0.
Interviewer Note:
CONTEXT- Tests understanding of base case handling and return values.
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