[Solved] Consider two approaches to solve Combination Sum (Reuse Allowed):... When is approach (2) preferable over (1)? | Subsets & Combinations

Subsets & Combinations - Combination Sum (Reuse Allowed)

Consider two approaches to solve Combination Sum (Reuse Allowed): (1) Backtracking with sorting and early pruning, and (2) Backtracking with frequency counting to avoid duplicates explicitly. When is approach (2) preferable over (1)?

AWhen input contains many duplicates and explicit frequency counting reduces redundant exploration

BWhen target is very small compared to candidates

CWhen candidates are unsorted and pruning is impossible

DWhen only one candidate is present

Step-by-Step Solution

Solution:

Step 1: Compare pruning vs frequency counting
Pruning helps early stop but does not avoid duplicate combinations if duplicates exist.
Step 2: Identify when frequency counting helps
Frequency counting explicitly avoids exploring duplicate combinations when input has duplicates.
Final Answer:
Option A -> Option A
Quick Check:
Frequency counting reduces duplicates in inputs with repeated candidates [OK]

Quick Trick: Frequency counting avoids duplicates in repeated inputs [OK]

Common Mistakes:

MISTAKES

Assuming pruning always suffices
Ignoring duplicates in input

Trap Explanation:

PITFALL

Candidates often overlook duplicate inputs and rely solely on pruning.

Interviewer Note:

CONTEXT

Tests understanding of trade-offs between pruning and frequency counting.

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When is approach (2) preferable over (1)?

Step 1: Compare pruning vs frequency counting

Step 2: Identify when frequency counting helps

Final Answer:

Quick Check:

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