Leetcode 46.Permutations(第十四周作业)

先贴原题：

Given a collection of distinct numbers, return all possible permutations.

For example, [1,2,3] have the following permutations:

[
[1,2,3],
[1,3,2],
[2,1,3],
[2,3,1],
[3,1,2],
[3,2,1]
]

这是一道典型的回溯题，通过不断递归即可找到所有解

class Solution(object):
def permute(self, nums):
""" :type nums: List[int] :rtype: List[List[int]] """
ret = []
def back(nums, p = []):
if not nums:
ret.append(p)
return
for i in range(len(nums)) :
back(nums[:i] + nums[i+1:], p + [nums[i]])
back(nums)
return ret