Serialize and Deserialize BST in Python

Suppose we want to design an algorithm to serialize and deserialize a binary search tree. Serialization is the process of converting something (data structure or object) into a sequence of bits so that it can be stored in a file or memory buffer, or transmitted across a network connection link. This can be reconstructed later that process is deserialization.

So, if the input is like [5,2,9,1,3,7], then the output will be Serialized output 5.2.9.1.3.7.N.N.N.N.N.N.N Deserialized output: 1, 2, 3, 5, 7, 9, (inorder traversal)

To solve this, we will follow these steps −

• Define a function serialize() . This will take root

• res := a new list

• define one queue and insert root

• while queue is non-empty, do

  • while queue is not empty, do

    • current := queue[0]

    • insert current at the end of res

    • delete first element from queue

    • if current is non-zero, then

      • come out from the loop

  • if current is null, then

    • come out from the loop

  • if current.left is not null, then

    • insert current.left at the end of queue

  • otherwise,

    • insert None at the end of queue

  • if current.right is not null, then

    • insert current.right at the end of queue

  • otherwise,

    • insert None at the end of queue

• s:= blank string

• for i in range 0 to size of res, do

  • if res[i] is non-zero, then

    • s := s concatenate res[i].data

  • otherwise,

    • s := s concatenate "N"

  • if i is same as size of res -1, then

    • come out from the loop

  • s := s concatenate "."

• return s

• Define a function deserialize() . This will take data

• data := a list of parts after dividing the data using dot

• stack := a new list

• if data[0] is same as 'N', then

  • return None

• root := create a new node with data data[0]

• insert root at the end of stack

• i := 1

• current := 0

• while i < size of data, do

  • left:= False

  • if data[i] is not same as 'N', then

    • temp := create a new node with data data[i]

    • stack[current].left := temp

    • insert temp at the end of stack

  • otherwise,

    • stack[current].left := None

  • i := i + 1

  • if data[i] is not same as 'N', then

    • temp := create a new node with data data[i]

    • stack[current].right := temp

    • insert temp at the end of stack

  • otherwise,

    • stack[current].right := None

  • current := current + 1

  • i := i + 1

• return root

Example 

Let us see the following implementation to get a better understanding −

 Live Demo

class TreeNode:
   def __init__(self, data, left = None, right = None):
      self.data = data
      self.left = left
      self.right = right
def insert(temp,data):
   que = []
   que.append(temp)
   while (len(que)):
      temp = que[0]
      que.pop(0)
      if (not temp.left):
         if data is not None:
            temp.left = TreeNode(data)
         else:
            temp.left = TreeNode(0)
         break
      else:
         que.append(temp.left)
      if (not temp.right):
         if data is not None:
            temp.right = TreeNode(data)
         else:
            temp.right = TreeNode(0)
         break
      else:
         que.append(temp.right)
def make_tree(elements):
   Tree = TreeNode(elements[0])
   for element in elements[1:]:
      insert(Tree, element)
   return Tree
def print_tree(root):
   #print using inorder traversal
   if root is not None:
      print_tree(root.left)
      print(root.data, end = ', ')
      print_tree(root.right)
class Codec:
   def serialize(self, root):
      res =[]
      queue = [root]
      while queue:
         while True and queue:
            current = queue[0]
            res.append(current)
            queue.pop(0)
            if current:
               break
         if not current:
            break
         if current.left:
            queue.append(current.left)
         else:
            queue.append(None)
         if current.right:
            queue.append(current.right)
         else:
            queue.append(None)
      s=""
      for i in range(len(res)):
         if res[i]:
            s+=str(res[i].data)
         else:
            s+="N"
         if i == len(res)-1:
            break
         s+="."
      return s
   def deserialize(self, data):
      data = data.split(".")
      stack = []
      if data[0]=='N':
         return None
      root = TreeNode(int(data[0]))
      stack.append(root)
      i = 1
      current = 0
      while i <len(data):
         left= False
         if data[i] !='N':
            temp = TreeNode(int(data[i]))
            stack[current].left = temp
            stack.append(temp)
         else:
            stack[current].left = None
         i+=1
         if data[i] !='N':
            temp = TreeNode(int(data[i]))
            stack[current].right = temp
            stack.append(temp)
         else:
            stack[current].right = None
         current+=1
         i+=1
         return root

ob = Codec()
root = make_tree([5,2,9,1,3,7])
ser = ob.serialize(root)
print('Serialization:',ser)
print_tree(ob.deserialize(ser))

Input

[5,2,9,1,3,7]

Output

Serialization: 5.2.9.1.3.7.N.N.N.N.N.N.N
1, 2, 3, 5, 7, 9,