Given an array of distinct integers, return all possible permutations.
Sample Output:
[[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]
Hints
Hint 1
Use backtracking to build permutations
Hint 2
Track used elements to avoid duplicates
Hint 3
Build permutations incrementally
