Serialize round trips

Questions 1 to 5 of 7

1. 1. What does this print? ``cpp auto t = node(8, node(3, leaf(1), nullptr), leaf(9)); std::cout << serialize(t.get()) << '\n'; ` node and leaf are the helpers from this lesson, and serialize writes the tree in preorder with #` markers for empty spots.

   8,3,1,#,#,9,#,#8,3,#,1,#,#,9,#,#8,3,1,#,#,#,9,#,#8,3,1,9,#,#,#,#,#
2. 2. What does this print? ``cpp auto r = deserialize("12abc,#,#"); std::cout << r->value << '\n'; ` deserialize is the reader from this lesson, and it reads each token with std::stoi`.

   throws an error, because abc is not a number12abc012
3. 3. A tree has 6 real nodes. How many # markers does its serialized text have?

   75136
4. 4. Two trees each have a root 1 and one child 2. In one, 2 is the left child. In the other, 2 is the right child. Which pair of texts from serialize tells them apart?

   Both are 1,2, because the values are the sameLeft child: 1,#,2,#,#. Right child: 1,2,#,#,#Left child: 1,2,#,#,#. Right child: 1,#,2,#,#Left child: 1,2,#,#. Right child: 1,#,2,#
5. 5. Spot the bug. This reader should rebuild the tree from 1,2,#,#,#, but writing the result back out gives 1,2,#,#,2,#,#. ``cpp std::unique_ptr<Node> read_node_wrong(const std::vector<std::string>& tokens, std::size_t pos) { if (pos >= tokens.size()) throw std::runtime_error("ran out of tokens"); const std::string& token = tokens[pos++]; if (token == "#") return nullptr; auto current = std::make_unique<Node>(std::stoi(token)); current->left = read_node_wrong(tokens, pos); current->right = read_node_wrong(tokens, pos); return current; } `` What is the bug?

   std::stoi should be std::stod, because the values can be negativemake_unique should be make_shared, so the children can be sharedpos is passed by value, so each call moves its own copy and the parent never sees how far the left subtree read, so the right child reads a token the left subtree already usedThe # check should come after pos++, so the marker is not counted