Which Tree traversal String is unique?

Assume we have a tree and we want to serialize it.

Example:

Tree
                              
      1                                                  
     / \                                                
    3   2                                       
   / \ / \                                 
  5  N N  N   
 / \
N   N

can result as:

"1,3,5,N,N,N,2,N,N", // Pre Order serialization;
"N,5,N,3,N,1,N,2,N", // In Order serialization;
"N,N,5,N,3,N,N,2,1", // Post Order serialization

I would like to know, which one of these three serializations is unique for all trees and why ?

Preorder traversal:

This traversals always yield unique binary trees. For a proof, please check why recording non-existent children in the pre-order traversal will differentiate different binary trees?.

For instance consider traversal sequence $6,5,N,N,5,3,N,N,2,N,N$.

We can proceed as follow to construct binary tree.

• First symbol is always root of tree.

Root will always be identified uniquely.

• Try to parse remaining part of input recursively(This will be our left sub-tree). When one sub-tree is parsed return.

Here this left sub-tree parsing will start with input $5,N,N,5,3,N,N,2,N,N$ and will return after input $5,3,N,N,2,N,N$ left to be processed.

• Try to parse yet remaining part of input recursively(This will be our right sub-tree).

Post-order traversal: This is similar to pre-order.

inorder traversal: This does not always yield unique binary tree. Here is counterexample.

Consider preorder traversal $N,5,N,6,N,3,N,5,N,2,N$. And following two binary trees.

6                    5
       /  \                /  \
      5    5              6    2
     / \  /  \           / \  / \
    N  N 3    2         5   3 N  N
        / \  / \       / \ / \
       N   N N  N     N  N N  N

StackExchange Computer Science Q#116655, answer score: 4