Permutations

All permutations with and without duplicates.

6 min readMastering Data Structures & Algorithms for Software Engineering InterviewsCode

Unique Elements

Backtrack by swapping: for each position, try all remaining elements by swapping. Restore after recursion.

Gopermutations-(swap-based).go

22 linesLn 1, Col 1Go

In-place swapping. Fix element at start, permute rest. Swap back after recursion. O(n! × n) time.

With Duplicates

Sort array first. Skip element if it's same as previous AND previous hasn't been used in current position (prevents duplicate permutations).

Gopermutations-with-duplicates.go

32 linesLn 1, Col 1Go

Used array tracks which indices in current permutation. Skip duplicate if previous identical element not used (would create same permutation).

Next Permutation

Find lexicographically next permutation in-place. Algorithm: 1) Find longest non-increasing suffix. 2) Find pivot (element before suffix). 3) Find rightmost successor to pivot in suffix. 4) Swap pivot and successor. 5) Reverse suffix.

Gonext-permutation.go

32 linesLn 1, Col 1Go

O(n) time, O(1) space. Find pivot, swap with next larger, reverse suffix for minimal increase.

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