A digital lock uses a set of unique digits, and each digit must be used exactly once to create a lock code.

Given an array digits of distinct integers, return all possible permutations of the digits.

Each permutation represents a possible lock code formed by rearranging all elements of the digits array.

You can return the answer in any order.

Example 1:

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

Explanation:
The digital lock has 3 unique digits: 1, 2, and 3.
Each lock code must use every digit exactly once.
If the first digit is 1, the remaining digits 2 and 3 can be arranged as
[1, 2, 3] and [1, 3, 2].
If the first digit is 2, the remaining digits 1 and 3 can be arranged as
[2, 1, 3] and [2, 3, 1].
If the first digit is 3, the remaining digits 1 and 2 can be arranged as
[3, 1, 2] and [3, 2, 1].
So, there are 3! = 3 × 2 × 1 = 6 possible lock codes.

Example 2:

Input: digits = [0, 4, 7, 9]
Output:
[
  [0, 4, 7, 9],    [4, 0, 7, 9],    [7, 0, 4, 9],    [9, 0, 4, 7],
  [0, 4, 9, 7],    [4, 0, 9, 7],    [7, 0, 9, 4],    [9, 0, 7, 4],
  [0, 7, 4, 9],    [4, 7, 0, 9],    [7, 4, 0, 9],    [9, 4, 0, 7],
  [0, 7, 9, 4],    [4, 7, 9, 0],    [7, 4, 9, 0],    [9, 4, 7, 0],
  [0, 9, 4, 7],    [4, 9, 0, 7],    [7, 9, 0, 4],    [9, 7, 0, 4],
  [0, 9, 7, 4],    [4, 9, 7, 0],    [7, 9, 4, 0],    [9, 7, 4, 0]
]

Explanation:
Each visual column groups permutations by the same first digit: 0, 4, 7, and 9.
For digits = [0, 4, 7, 9], there are 4 distinct digits:
4! = 4 × 3 × 2 × 1 = 24
So, the output contains 24 permutations.

Example 3:

Input: digits = [5]
Output:
[
  [5]
]

Explanation:
There is only one digit, so there is only one possible lock code.
The digit 5 must be used exactly once, so the only permutation is [5].

Constraints

1 <= digits.length <= 6

0 <= digits[i] <= 9

All integers in digits are unique.

64. Permutations