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]
]

记录一下自己的思路总结，关于去重复的思路比较棒：

全排序一：

class Solution(object):   
    def permute(self, nums):
        """
        :type nums: List[int]
        :rtype: List[List[int]]
        全排序
        """
        self.result = []
        self.permutation(nums,0)
#         print(self.result)
#         st = {tuple(i) for i in self.result}
#         l = [list(i) for i in st]
        return self.result
        
    def permutation(self,nums,start):
        length = len(nums)
        if start == length-1:
#             print(nums)
            n = nums[:]
            self.result.append(n)

        for i in range(start,length):

            nums = self.swap(nums,start,i)
            self.permutation(nums,start+1)
            nums = self.swap(nums,start,i)
                
    def swap(self,l,start,end):
        l[start],l[end] = l[end],l[start]
        return l

　　

全排序二：

有两种方式，更好的肯定是从底层就不交换大大节约时间，无脑的则是先全排列，后集合去重。

class Solution(object):
    def permuteUnique(self, nums):
        """
        全排列2集合去重复
        :type nums: List[int]
        :rtype: List[List[int]]
        """
        self.result = []
        self.permutation(nums,0)
#         print(self.result)
        st = {tuple(i) for i in self.result}
        l = [list(i) for i in st]
        return l
        
    def permutation(self,nums,start):
        length = len(nums)
        if start == length-1:
#             print(nums)
            n = nums[:]
            self.result.append(n)

        for i in range(start,length):

            nums = self.swap(nums,start,i)
            self.permutation(nums,start+1)
            nums = self.swap(nums,start,i)
                
    def swap(self,l,start,end):
        l[start],l[end] = l[end],l[start]
        return l       

　　

class Solution(object):
    def permuteUnique(self, nums):
        """
        全排列2优化
        :type nums: List[int]
        :rtype: List[List[int]]
        """
        self.result = []
        self.permutation(nums,0)
#         print(self.result)

        return self.result
        
    def permutation(self,nums,start):
        length = len(nums)
        if start == length-1:
#             print(nums)
            n = nums[:]
            self.result.append(n)
        temp = []
        for i in range(start,length):
            if nums[i] not in temp:
                temp.append(nums[i])
                nums = self.swap(nums,start,i)
                self.permutation(nums,start+1)
                nums = self.swap(nums,start,i)
                
    def swap(self,l,start,end):
        l[start],l[end] = l[end],l[start]
        return l