Serialize-Deserialize a BT / BST

SerializeDeserializeBT.py

# Leetcode : 449
# 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: Optional[TreeNode]) -> str:
        """
            Encodes a tree to a single string.
        """
        data = []

        def preorder(node: Optional[TreeNode]):
            nonlocal data
            # Node -> Left -> Right
            data.append(f"{node.val}" if node else "X")
            if node:
                preorder(node.left)
                preorder(node.right)
            return

        preorder(root)

        return ":".join(data)


    def deserialize(self, data: str) -> Optional[TreeNode]:
        """
            Decodes your encoded data to tree.
        """
        data = data.split(":")
        n = len(data)
        i = 0

        def preorder():
            nonlocal i
            if i < n:
                v = data[i]
                i = i + 1
                if "X" != v:
                    node = TreeNode(v)
                    node.left = preorder()
                    node.right = preorder()
                    return node
            return None

        return preorder()


# 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