Tree: Depth-First Search - Flatten Binary Tree to Linked List
Consider the optimal flatten function using reverse preorder traversal with a global pointer. What is the output linked list when the input tree is a single node with value 42?
Consider the optimal flatten function using reverse preorder traversal with a global pointer. What is the output linked list when the input tree is a single node with value 42?
medium🧾 Code Trace Q4 of Q15
Step-by-Step Solution
Solution:
Step 1: Trace flatten on single node
Recursion calls flatten on None children, returns immediately.Step 2: Pointer rewiring
Node's right pointer set to prev (None), left pointer set to None, prev updated to node.Final Answer:
Option D -> Option DQuick Check:
Single node remains as is in linked list [OK]
Quick Trick: Single node flatten returns node itself [OK]
Common Mistakes:
MISTAKES- Expecting extra None in output
- Confusing empty list with single node
Trap Explanation:
PITFALL- Candidates sometimes think output includes None explicitly or empty list for single node.
Interviewer Note:
CONTEXT- Tests handling of minimal edge case input.
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