全排列46

class :
    def permute(self, nums):
        """
        :type nums: List[int]
        :rtype: List[List[int]]
        """
        n = len(nums)
        
        if n <= 1:
            return [nums]
        res = []
        for i in range(n):
            nums_copy = nums.copy()
            sub_res = [nums_copy.pop(i)]
            s = self.permute(nums_copy)
            a = [sub_res + j for j in s]
            # 递归过程
            sub_res.extend(self.permute(nums_copy))
            for k in a:
                if not k in res:
                    res.append(k)
        return res

# 例子
a = [1, 2, 3]
print(Solution().permute(a))