Serialize and deserialize BST

Time: O(N); Space: O(H); medium

Serialization is the process of converting a 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 to be reconstructed later in the same or another computer environment.

Design an algorithm to serialize and deserialize a binary search tree.

There is no restriction on how your serialization/deserialization algorithm should work.

You just need to ensure that a binary search tree can be serialized to a string and this string can be deserialized to the original tree structure.

The encoded string should be as compact as possible.

Example 1:

  2
 / \
1   3

Input：root = {TreeNode} [2,1,3]

Output：“2 1 3” -> {TreeNode} [2,1,3]

Example 2:

1
 \
  2

Input：root = {TreeNode} [1,#,2]

Output：“1 2” -> {TreeNode} [1,#,2]

Note:

  • Do not use class member/global/static variables to store states. Your serialize and deserialize algorithms should be stateless.

[6]:

class TreeNode(object):
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None

[7]:

import collections

class Codec(object):

    def serialize(self, root):
        """
        Encodes a tree to a single string.
        :type root: TreeNode
        :rtype: str
        """
        def serializeHelper(node, vals):
            if node:
                vals.append(node.val)
                serializeHelper(node.left, vals)
                serializeHelper(node.right, vals)

        vals = []
        serializeHelper(root, vals)

        return ' '.join(map(str, vals))


    def deserialize(self, data):
        """
        Decodes your encoded data to tree.
        :type data: str
        :rtype: TreeNode
        """
        def deserializeHelper(minVal, maxVal, vals):
            if not vals:
                return None

            if minVal < vals[0] < maxVal:
                val = vals.popleft()
                node = TreeNode(val)

                node.left = deserializeHelper(minVal, val, vals)
                node.right = deserializeHelper(val, maxVal, vals)

                return node
            else:
                return None

        vals = collections.deque([int(val) for val in data.split()])

        return deserializeHelper(float('-inf'), float('inf'), vals)

[8]:

c = Codec()

root = TreeNode(2)
root.left = TreeNode(1)
root.right = TreeNode(3)
res_str = c.serialize(root)
assert res_str == "2 1 3"
res_node = c.deserialize(res_str)
assert res_node.val == 2
assert res_node.left.val == 1
assert res_node.right.val == 3

root = TreeNode(1)
root.right = TreeNode(2)
res_str = c.serialize(root)
assert res_str == "1 2"
res_node = c.deserialize(res_str)
assert res_node.val == 1
assert res_node.right.val == 2