Which modification to the original DFS approach correctly solves this variant?
hard🎤 Interviewer Follow-up Q15 of Q15
Tree: Depth-First Search - Symmetric Tree (DFS Approach)
Suppose the problem is extended: the tree nodes can have duplicate values, and you want to check if the tree is symmetric ignoring node values, only structure matters. Which modification to the original DFS approach correctly solves this variant?
AKeep the value comparison but add a hash map to track visited nodes to avoid duplicates.
BUse BFS level-order traversal and check if each level forms a palindrome of node values.
CModify the base case to return true if both nodes are null, and skip the value comparison step entirely.
DPerform a preorder traversal and compare the traversal list with its reverse.
Step-by-Step Solution
Solution:
Step 1: Understand the variant ignores node values, only structure matters
Therefore, the value comparison step must be removed to avoid false negatives due to duplicates.
Step 2: Modify the DFS to only check if both nodes exist or are null, recursively comparing mirrored subtrees
Return true if both nodes are null; otherwise, recurse on mirrored children without comparing values.
Final Answer:
Option C -> Option C
Quick Check:
Ignoring values means skipping value checks but preserving mirrored structure checks [OK]
Quick Trick:Ignore values, check only mirrored structure recursively [OK]
Common Mistakes:
MISTAKES
Keeping value checks causing false negatives
Using BFS palindrome checks which fail on structure
Using preorder traversal which ignores mirrored structure
Trap Explanation:
PITFALL
Keeping value checks or using BFS palindrome seems plausible but breaks structural-only symmetry.
Interviewer Note:
CONTEXT
Tests candidate's ability to adapt DFS logic to problem variants ignoring node values.
Master "Symmetric Tree (DFS Approach)" in Tree: Depth-First Search
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