Permutations

Problem

Given an array nums of distinct integers, return all the possible permutations. You can return the answer in any order.

Input / Output Format

Input: Array of unique integers nums. Output: List of all permutations (each is a list of integers).

Examples

Example 1

Input: nums = [1,2,3] Output: [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]

Example 2

Input: nums = [0,1] → Output: [[0,1],[1,0]]

Example 3

Input: nums = [1] → Output: [[1]]

Approach Hints

• Backtracking — Maintain a current list and a used boolean array. For each unused element, append to current, recurse, then pop & unmark. Base case: len(current) == n → push a copy. Time: O(n · n!) (n! permutations, n work to copy).
• Heap's Algorithm — In-place swap-based, O(n!) generations.
• Pitfall: appending the same list reference; always push a copy.