class Codec:
    def serialize(self, root: TreeNode | None) -> str:
        result = []
        def preorder(node):
            if not node:
                result.append('null')
                return
            result.append(str(node.val))
            preorder(node.left)
            preorder(node.right)
        preorder(root)
        return ','.join(result)

    def deserialize(self, data: str) -> TreeNode | None:
        values = iter(data.split(','))
        def build():
            val = next(values)
            if val == 'null':
                return None
            node = TreeNode(int(val))
            node.left = build()
            node.right = build()
            return node
        return build()
Trees — DFS, BFS, BST

Trees — DFS, BFS, BST

Trees — DFS, BFS, BST
