How do you convert a binary tree into a doubly linked list?
Direct Answer
This problem tests the ability to modify tree structures in-place to create linear data structures. It requires deep understanding of pointer manipulation and recursion.
Why Interviewers Ask This
This question assesses advanced pointer manipulation skills and the ability to restructure data without allocating new nodes. It demonstrates whether a candidate can perform complex in-place transformations efficiently.
How to Answer This Question
Describe using an in-order traversal to visit nodes sequentially. Maintain a reference to the previously visited node to link it to the current node. Update both left and right pointers to form the DLL. Handle the head of the list carefully during the recursion.
Key Points to Cover
- Use in-order traversal sequence
- Maintain previous node pointer
- Modify pointers in-place
- Return correct head node
Sample Answer
I would perform an in-order traversal recursively. During the traversal, I keep a global pointer to the previous node. For each current node, I set its left pointer to the previous node and the previous node's right poin…
Common Mistakes to Avoid
- Creating new nodes instead of modifying existing ones
- Losing the head reference
- Incorrectly linking left and right pointers
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