text: class Solution:
      def combine(self, n: int, k: int) -> List[List[int]]:
          results = []
          
          def rec(sub, partial):
              if len(partial) == k:
                  results.append(list(partial))
                  return
              
              if n + 1 == sub:
                  return
              
              rec(sub + 1, partial)
              
              partial.append(sub)
              rec(sub + 1, partial)
              partial.pop()
              
          rec(1, [])
          
          return results