Serialize round trips

Questions 1 to 5 of 7

1. 1. The serialize function from this lesson runs on this tree. What does it print? ``python tree = TreeNode(5, TreeNode(3, None, TreeNode(4)), TreeNode(8)) print(serialize(tree)) ``

   5,3,4,8,null,null,null,null,null5,3,null,null,4,null,null,8,null5,3,null,4,null,null,8,null,null5,null,3,4,null,null,8,null,null
2. 2. The read_preorder function from this lesson runs on the words below and then prints two lines. What is the second line? ``python from collections import deque tokens = deque('1,2,null,null,3,null,null,9'.split(',')) root = read_preorder(tokens) print(f'root {root.val}, right {root.right.val}') print(f'words left: {len(tokens)}, first left: {tokens[0]}') ``

   words left: 1, first left: 9words left: 0, first left: nullwords left: 2, first left: 9words left: 1, first left: null
3. 3. Why does the writer add the word null for an empty tree, instead of writing an empty string?

   An empty string cannot be saved to a fileThe reader needs a word to take, and an empty string gives it no marker that says the tree is emptyThe split method cannot read an empty stringThe word null makes the text shorter than an empty string
4. 4. A tree has 9 real nodes. How many null words does its serialized text contain?

   891810
5. 5. This reader has the check for the word null removed. It is given the words of 1,2,null,null,3,null,null. What happens? ``python def read_preorder(tokens): token = tokens.popleft() node = TreeNode(int(token)) node.left = read_preorder(tokens) node.right = read_preorder(tokens) return node ``

   It raises ValueError when it reaches the word nullIt returns the tree 1(2, 3) with no errorIt raises IndexError after the last wordIt loops forever