How to Serialize Binary Tree

Question

I went to an interview today where I was asked to serialize a binary tree. I implemented an array-based approach where the children of node i (numbering in level-order trave

Answer 1

Here is a late answer in Python. It uses (depth-first) preorder serialization and returns a list of strings. Deserialization returns the tree.

class Node:
    def __init__(self, val, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right


# This method serializes the tree into a string
def serialize(root):
    vals = []
    def encode(node):
        vals.append(str(node.val))
        if node.left is not None:
            encode(node.left)
        else:
            vals.append("L")
        if node.right is not None:
            encode(node.right)
        else:
            vals.append("R")
    encode(root)
    print(vals)
    return vals


# This method deserializes the string back into the tree
def deserialize(string_list):
    def create_a_tree(sub_list):
        if sub_list[0] == 'L' or sub_list[0] == 'R':
            del sub_list[0]
            return None
        parent = Node(sub_list[0])
        del sub_list[0]
        parent.left = create_a_tree(sub_list)
        parent.right = create_a_tree(sub_list)
        return parent
    if len(string_list) != 0:
        root_node = create_a_tree(string_list)
    else:
        print("ERROR - empty string!")
        return 0
    return root_node

To test:

tree1 = Node('root', Node('left'), Node('right'))
t = deserialize(serialize(tree1))
print(str(t.right.val))