Serialized Tree Representation

A common approach to use a vector to represent a binary tree is serialized representation. All LeetCode OJ use this kind of representation: the serialization of a binary tree follows a level order traversal, where '#' signifies a path terminator where no node exists below.

Here's an example:

   1
  / \
 2   3
    /
   4
    \
     5

The above binary tree is serialized as "{1,2,3,#,#,4,#,#,5}".

For testing propose, I tried to write transform functions between serialized tree and binary tree. Essentially we could use level order traversal. The following class provides several methods to implement this.