serialize-and-deserialize-bst.py

# Time:  O(n)
# Space: O(h)

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

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Codec:

    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)


# Your Codec object will be instantiated and called as such:
# codec = Codec()
# codec.deserialize(codec.serialize(root))