[LeetCode]46. 全排列

46. 全排列
给定一个没有重复数字的序列，返回其所有可能的全排列。
示例:
输入: [1,2,3]
输出:
[
[1,2,3],
[1,3,2],
[2,1,3],
[2,3,1],
[3,1,2],
[3,2,1]
]

解法1

class Solution:
    def permute(self, nums):
        if len(nums) <= 1:
            return [nums]
        
        res = [[nums[0]]]
        index = 1
        while index < len(nums):
            tmp = []
            for each in res:
                for i in range(index+1):
                    tmp.append(each[:i]+[nums[index]]+each[i:])
            res = tmp
            index += 1
        return res

解法2

class Solution:
    def permute(self, nums):
       if len(nums) <= 1:
            return [nums]
        
        res = []
        perms = self.permute(nums[1:])
        for each in perms:
            for i in range(len(each)+1):
                p = each[:i]+[nums[0]]+each[i:]
                res.append(p)
        return res

解法3

用itertools库的permutations函数.

import itertools
class Solution:
    def permute(self, nums):
        return list(itertools.permutations(nums))

基本思路都是用DFS算法+交换数字的方式。还有更多全排列的题请参考：
https://blog.csdn.net/jacky_chenjp/article/details/66477538