new_contents: def distance(first_strand, second_strand):
    if len(first_strand) != len(second_strand):
      raise ValueError()
  
    hamming_distance = 0
    for i in range(len(first_strand)):
      if first_strand[i] != second_strand[i]:
        hamming_distance += 1
  
    return hamming_distance
  
subject: add hamming solution