Serialize and Deserialize Binary Tree

Description

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 tree. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that a binary tree can be serialized to a string and this string can be deserialized to the original tree structure.

For example, you may serialize the following tree

1

/ \ 2 3 / \ 4 5 as "[1,2,3,null,null,4,5]", just the same as how LeetCode OJ serializes a binary tree. You do not necessarily need to follow this format, so please be creative and come up with different approaches yourself.

Hint

Train of Thought

The idea is simple: print the tree in pre-order traversal and use "X" to denote null node and split node with ",". We can use a StringBuilder for building the string on the fly. For deserializing, we use a Queue to store the pre-order traversal and since we have "X" as null node, we know exactly how to where to end building subtress.

Code

public String serialize(TreeNode root) {
        return serial(new StringBuilder(), root).toString();
    }

    private StringBuilder serial(StringBuilder str, TreeNode root) {
        if (root == null) return str.append("#");
        str.append(root.val).append(",");
        serial(str, root.left).append(","); // note execution order
        return serial(str, root.right);
    }

    public TreeNode deserialize(String data) {
        return deserial(new LinkedList<>(Arrays.asList(data.split(","))));
    }

    private TreeNode deserial(Queue<String> queue) {
        String val = queue.poll(); // return null if empty
        if ("#".equals(val)) return null;
        TreeNode root = new TreeNode(Integer.valueOf(val));
        root.left = deserial(queue);
        root.right = deserial(queue);
        return root;
    }

Complexity

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