LeetCode 297. Serialize and Deserialize Binary Tree

Question

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.

Clarification: The input/output format is the same as how LeetCode serializes a binary tree. You do not necessarily need to follow this format, so please be creative and come up with different approaches yourself.

Example 1:

1 2	Input: root = [1,2,3,null,null,4,5] Output: [1,2,3,null,null,4,5]

Example 2:

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

Example 3:

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

Solution

Solution1 – preorder traversal

public class Codec {

    // Encodes a tree to a single string.
    public String serialize(TreeNode root) {
        if (root == null) return "#";
        return root.val + "," + serialize(root.left) + "," + serialize(root.right);
    }

    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        Queue<String> q = new LinkedList<>(Arrays.asList(data.split(",")));
        return helper(q);
    }
    private TreeNode helper(Queue<String> q){
        String s = q.poll();
        if (s.equals("#")) return null;
        TreeNode root = new TreeNode(Integer.parseInt(s));
        root.left = helper(q);
        root.right = helper(q);
        return root;
    }
}

Complexity:

Time complexity: O(n)

Space complexity: O(n)