全排列

给出一个列表[1,2,3]，其全排列为：

[
[1,2,3],
[1,3,2],
[2,1,3],
[2,3,1],
[3,1,2],
[3,2,1]
]
和子集的差别就是一个start，一个是visited数组
https://www.lintcode.com/zh-cn/problem/permutations/

def subjectHelper(self, nums, visited):
        if len(self.result) == len(nums):
            self.resultAll.append(list(self.result))
        for i in range(len(nums)):
            if visited[i]:
                continue
            self.result.append(nums[i])
            visited[i] = True
            self.subjectHelper(nums, visited)
            visited[i] = False
            self.result.pop(-1)
        
    def permute(self, nums):
        # write your code here
        n = len(nums)
        if n == 0:
            return []
        self.result = []
        self.resultAll = []
        self.subjectHelper(nums, [False]*n)
        return self.resultAll