old_contents: """
  There is an array of non-negative integers.
  A second array is formed by shuffling the elements of the first array and deleting a random element.
  Given these two arrays, find which element is missing in the second array.
  http://www.ardendertat.com/2012/01/09/programming-interview-questions/
  """
  
  def findMissingNumber3(array1, array2):
      result=0 
      for num in array1+array2:
          result^=num 
      return result
  
new_contents: """
  There is an array of non-negative integers.
  A second array is formed by shuffling the elements of the first array and
  deleting a random element.
  Given these two arrays, find which element is missing in the second array.
  http://www.ardendertat.com/2012/01/09/programming-interview-questions/
  """
  
  
  def findMissingNumber(array1, array2):
      result = 0
      for num in array1 + array2:
          result ^= num
      return result
  
subject: fix elements