Combinations

Combinations of k from n, combination sum variants.

6 min readMastering Data Structures & Algorithms for Software Engineering InterviewsCode

Combinations (k from n)

Choose k elements from 1..n. Backtrack: try including each number from start to n, recurse with start+1.

Gocombinations.go

27 linesLn 1, Col 1Go

Start from 1, recurse with i+1. Prune when not enough remaining elements to reach k.

Combination Sum

Find all unique combinations of candidates that sum to target. Each candidate can be used unlimited times. Sort candidates, backtrack with start index (allow reuse by passing i, not i+1).

Gocombination-sum.go

25 linesLn 1, Col 1Go

Pass i (not i+1) to allow reuse. Sort enables pruning: break when candidate > remaining.

Combination Sum II

Each candidate used at most once. Similar to combination sum but pass i+1. Skip duplicates: if same as previous AND previous not used in this position, skip.

Gocombination-sum-ii.go

26 linesLn 1, Col 1Go

i+1 prevents reuse. Skip duplicates: if same as previous AND we're at same recursion level (i > start), skip to avoid duplicate combinations.

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