Given the following code for inverting a binary tree, what is the value of the left child of the root node after calling invertTree(root) on the tree below? Tree structure before inversion:

easy🧾 Code Trace Q12 of Q15

Tree: Depth-First Search - Invert Binary Tree

Given the following code for inverting a binary tree, what is the value of the left child of the root node after calling invertTree(root) on the tree below? Tree structure before inversion:

    2
   / \
  1   3

Dnull

Step-by-Step Solution

Step 1: Trace recursive calls on root=2
invertTree called on left child (1) and right child (3), both leaves, so their children are null and return immediately.
Step 2: Swap left and right children of root=2
After recursion, root.left and root.right are swapped: left becomes 3, right becomes 1.
Final Answer:
Option A -> Option A
Quick Check:
Root's left child after inversion is original right child 3 [OK]

Quick Trick: Swapping children after recursion flips subtree positions [OK]

Common Mistakes:

MISTAKES

Confusing left and right child values after inversion
Forgetting to swap after recursive calls
Assuming root value changes

Trap Explanation:

PITFALL

Candidates often forget that swapping happens after recursion, so left child becomes original right child.

Interviewer Note:

CONTEXT

Checks ability to mentally execute recursion and swapping order.

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Given the following code for inverting a binary tree, what is the value of the left child of the root node after calling invertTree(root) on the tree below? Tree structure before inversion:

Step 1: Trace recursive calls on root=2

Step 2: Swap left and right children of root=2

Final Answer:

Quick Check:

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