python leetcode 46. Permutations

# Given a collection of distinct integers, return all possible permutations.
"""
给定一组不同的整数，返回所有可能的排列。
Input: [1,2,3]
Output: [[1,2,3], [1,3,2], [2,1,3], [2,3,1], [3,1,2], [3,2,1]]
"""
class Solution(object):
    def permute(self, nums):
        """
        :type nums: List[int]
        :rtype: List[List[int]]
        """
        if len(nums) <= 1:
            return [nums]
        ans = []
        for i, num in enumerate(nums):
            rest_num = nums[:i] + nums[i+1:]
            for j in self.permute(rest_num):
                ans.append([num] + j)
        return ans