text: def findRanges(nums):
      interval = 3
      num_groups = round((max(nums) - min(nums)) / interval, 0)
      
      ranges = []
      for i in range(min(nums),max(nums),interval+1):
          r = str(i) + '->' + str(i+interval)
          ranges.append(r)
      return ranges
  
  
  if __name__ == '__main__':
      print(findRanges([0, 1, 2, 5, 7, 8, 9, 9, 10, 11, 15]))
      # ['0->2', '5->5', '7->11', '15->15']
  