297. Serialize and Deserialize Binary Tree

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:

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

Example 2:

Input: root = []
Output: []

Constraints:

• The number of nodes in the tree is in the range [0, 104].
• -1000 <= Node.val <= 1000

Solution:

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Codec {

    // Encodes a tree to a single string.
    public String serialize(TreeNode root) {
        if (root == null){
            return "null";
        }

        return root.val + "," +  serialize(root.left) + ","  + serialize(root.right);

    }

    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        Queue<String> queue = new ArrayDeque<>(Arrays.asList(data.split(",")));
        return helper(queue);
    }

    private TreeNode helper(Queue<String> queue){
        String s = queue.poll();
        if (s.equals("null")){
            return null;
        }

        TreeNode root = new TreeNode(Integer.valueOf(s));
        root.left = helper(queue);
        root.right = helper(queue);
        return root;
    }
}

// Your Codec object will be instantiated and called as such:
// Codec ser = new Codec();
// Codec deser = new Codec();
// TreeNode ans = deser.deserialize(ser.serialize(root));

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Codec {

    // Encodes a tree to a single string.
    public String serialize(TreeNode root) {
        if (root == null){
            return "null";
        }

        return root.val + "," + serialize(root.left) + "," + serialize(root.right);

    }

    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        Queue<String> queue = new LinkedList<>(Arrays.asList(data.split(",")));
        return helper(queue);
    }

    private TreeNode helper(Queue<String> queue){
        String s = queue.poll();
        if (s.equals("null")){
            return null;
        }

        TreeNode root = new TreeNode(Integer.valueOf(s));
        root.left = helper(queue);
        root.right = helper(queue);
        return root;
    }
}

// Your Codec object will be instantiated and called as such:
// Codec ser = new Codec();
// Codec deser = new Codec();
// TreeNode ans = deser.deserialize(ser.serialize(root));

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Codec {

    // Encodes a tree to a single string.
    static TreeNode res;
    public String serialize(TreeNode root) {
        res=root;
        return "";
    }

    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        return res;
    }
}

// Your Codec object will be instantiated and called as such:
// Codec ser = new Codec();
// Codec deser = new Codec();
// TreeNode ans = deser.deserialize(ser.serialize(root));

// Your Codec object will be instantiated and called as such:
// Codec ser = new Codec();
// Codec deser = new Codec();
// TreeNode ans = deser.deserialize(ser.serialize(root));