Permutations

1class Solution:
2    def permute(self, nums: List[int]) -> List[List[int]]:
3        results = []
4        def backtrack(start_index, used, path):
5            if len(path) == len(nums):
6                results.append(path)
7                return
8
9            for i, num in enumerate(nums):
10                if used[i]:
11                    continue
12                used[i] = True
13                backtrack(start_index + 1, used, path + [num])
14                used[i] = False
15        
16        backtrack(0, defaultdict(bool), [])
17        return results