text: def sum_zero(array1):
      # Loop element from left of array and from the right of array
      # If right < left, return None
      # else if element at index left + element at index right == 0, return array1[left] and  array1[right]
      # else return None
      left = 0
      right = len(array1) - 1
      sum_num = 0
      while right >= left:
          #print(array1[left])
          #print(array1[right])
          sum_num = array1[left] + array1[right]
          if sum_num == 0:
              if left == right:
                  return [array1[left]]
              else:
                  return [array1[left], array1[right]]
          elif sum_num>0:
              right = right - 1
          else:
              left = left + 1
  
      return None
  
  
  print(sum_zero([-3, -2, -1, 0, 1, 2, 3]))
  print(sum_zero([-2, 0, 1, 3]))
  print(sum_zero([1, 2, 3]))
  print(sum_zero([0]))
  