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If the flatten algorithm is modified to allow nodes to appear multiple times in the flattened linked list, which change is required?

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Tree: Depth-First Search - Flatten Binary Tree to Linked List
If the flatten algorithm is modified to allow nodes to appear multiple times in the flattened linked list, which change is required?
AImplement a mechanism to clone nodes before linking
BUse a global pointer to track previously visited nodes
CTraverse the tree in inorder instead of preorder
DSet all left pointers to point to the parent node
Step-by-Step Solution
Solution:

  1. Step 1: Understand node reuse

    Allowing nodes multiple times means the same node instance cannot be reused directly.

  2. Step 2: Cloning nodes

    To have duplicates, nodes must be cloned to create distinct instances.

  3. Step 3: Algorithm modification

    Modify flatten to clone nodes before linking to the list.

  4. Final Answer:

    Option A -> Option A

  5. Quick Check:

    Duplicates require distinct node instances [OK]
Quick Trick: Duplicates need cloned nodes, not reused ones [OK]
Common Mistakes:
MISTAKES
  • Reusing same nodes causing cycles
  • Changing traversal order without cloning
  • Misusing left pointers to create duplicates
Trap Explanation:
PITFALL
  • Reusing nodes causes incorrect linked list with cycles or shared nodes
Interviewer Note:
CONTEXT
  • Tests ability to adapt algorithm for node duplication requirements
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