Given the following prefix_counts hash map state during DFS traversal: {0:1, 5:1, 8:1}, and current_sum = 8, targetSum = 3, which node values could have led to this state assuming the path from root to current node?

hard🔄 Reverse Engineer Q9 of Q15

Tree: Depth-First Search - Path Sum III (Any Path)

ANode values along path: 8, 0

BNode values along path: 3, 5

CNode values along path: 5, 3

DNode values along path: 0, 3, 5

Step-by-Step Solution

Solution:

Step 1: Understand prefix_counts keys
Keys represent cumulative sums along the path: 0 (empty), 5, and 8.
Step 2: Deduce node values
From 0 to 5 means first node val=5, then from 5 to 8 means next node val=3, so path is 5->3.
Final Answer:
Option C -> Option C
Quick Check:
Prefix sums increase by node values along path [OK]

Quick Trick: Prefix sums are cumulative sums of node values along path [OK]

Common Mistakes:

MISTAKES

Mixing order of node values
Confusing prefix sums with node values

Trap Explanation:

PITFALL

Candidates often confuse prefix sums with node values or reverse order of nodes.

Interviewer Note:

CONTEXT

Tests ability to reverse engineer prefix sums to original node values.

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Given the following prefix_counts hash map state during DFS traversal: {0:1, 5:1, 8:1}, and current_sum = 8, targetSum = 3, which node values could have led to this state assuming the path from root to current node?

Step 1: Understand prefix_counts keys

Step 2: Deduce node values

Final Answer:

Quick Check:

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