text:  class Solution:
      def XXX(self, nums: List[int]) -> List[List[int]]:
  
          res = [] 
          def backtrack(k, t):
              if len(t) == len(nums):
                  import copy
                  res.append(copy.deepcopy(t))
                  return 
              for i in range(len(nums)):
                  if nums[i] in t:continue 
                  t = t + [nums[i]] 
                  backtrack(i, t)
                  t.pop(-1)
          backtrack(0,[])
          return res 
  
  