new_contents: class Solution:
      # @param {integer[]} nums
      # @return {integer[][]}
      def permute(self, nums):
          if len(nums) == 0:
              return nums
          if len(nums) == 1:
              return [nums]
          res = []
          for i in range(len(nums)):
              tmp = nums[:]
              head = tmp.pop(i)
              tail = self.permute(tmp)
              
              [ t.insert(0, head) for t in tail]
              res.extend(tail[:])
          return res
  
subject: Create Perm_002.py