# LeetCode 46. Permutations

## Description

https://leetcode.com/problems/permutations/

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

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 = 
Output: []
```

Constraints:

• `1 <= nums.length <= 6`
• `-10 <= nums[i] <= 10`
• All the integers of `nums` are unique.

## Explanation

Use backtracking to find all permutations. If the element has been visited, we can skip searching next permutations.

## Python Solution

``````class Solution:
def permute(self, nums: List[int]) -> List[List[int]]:
results = []

visited = set()
self.helper(results, nums, [], 0, visited)

return results

def helper(self, results, nums, combination, start, visited):
if len(combination) == len(nums):
results.append(list(combination))
return

for i in range(len(nums)):
if nums[i] in visited:
continue

1. Tuba says: