449. Serialize and Deserialize BST.md

449. Serialize and Deserialize BST

https://leetcode.com/problems/serialize-and-deserialize-bst/

Serialization is 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 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:

Input: root = [2,1,3]
Output: [2,1,3]

Example 2:

Input: root = []
Output: []

Constraints:

• The number of nodes in the tree is in the range [0, 104].
• 0 <= Node.val <= 104
• The input tree is guaranteed to be a binary search tree.

代码

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

class Codec:

    def serialize(self, root: TreeNode) -> str:
        """Encodes a tree to a single string.
        """
        path = []
        def preorder(node):
            if node:
                path.append(node.val)
                preorder(node.left)
                preorder(node.right)
        preorder(root)
        return "#".join(map(str, path))
        

    def deserialize(self, data: str) -> TreeNode:
        """Decodes your encoded data to tree.
        """
        
        if not data:
            return None
        values = deque([int(val) for val in data.split('#')])
        def build(left, right):
            if values and left < values[0] < right:
                node_value = values.popleft()
                node = TreeNode(node_value)
                
                node.left = build(left, node_value)
                node.right = build(node_value, right)
                
                return node
        return build(float('-inf'), float('inf'))
        

# Your Codec object will be instantiated and called as such:
# Your Codec object will be instantiated and called as such:
# ser = Codec()
# deser = Codec()
# tree = ser.serialize(root)
# ans = deser.deserialize(tree)
# return ans