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Given the final output of the Combination Sum II function for candidates = [1,1,2,5,6,7,10] and target = 8 is [[1,1,6],[1,2,5],[1,7],[2,6]], which candidate was NOT used in any combination?

hard🔄 Reverse Engineer Q9 of Q15

Subsets & Combinations - Combination Sum II (No Reuse, Duplicates)

Given the final output of the Combination Sum II function for candidates = [1,1,2,5,6,7,10] and target = 8 is [[1,1,6],[1,2,5],[1,7],[2,6]], which candidate was NOT used in any combination?

A10

B6

C7

D1

Step-by-Step Solution

Solution:

Step 1: Review output combinations
All combinations sum to 8 and include 1,2,5,6,7 but none include 10.
Step 2: Confirm candidate usage
Candidate 10 is never used because it exceeds or cannot fit into target 8 with others.
Final Answer:
Option A -> Option A
Quick Check:
10 is excluded from all valid combinations [OK]

Quick Trick: Check output combos to find unused candidates [OK]

Common Mistakes:

MISTAKES

Assuming all candidates appear in output
Ignoring candidates too large for target

Trap Explanation:

PITFALL

Candidates often assume all input numbers appear in output combinations.

Interviewer Note:

CONTEXT

Tests ability to reason backward from output to input usage.

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