449. Serialize and Deserialize BST

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
/*
Serialize function
Time Complexity: O(M * K) = O(M * 11) = O(M)
Space Complexity: O(M * K) = O(M * 11) = O(M)
M = Number of Nodes
K = Average Length of each node. (Bounded by 11)

Deserialize function
Time Complexity: O(N + M + M*K) = O(N + M*K) = O(N+N) = O(N)
Space Complexity: O(M * K) = O(N)
N = Length of the input string
M = Number of Nodes
K = Average Length of each node. (Bounded by 11)
*/
public class Codec {

    // Encodes a tree to a single string.
    public String serialize(TreeNode root) {
        if (root == null) {
            return "";
        }
        List<String> list = new ArrayList();
        serializeHelper(list, root);
        return String.join(",", list);
    }

    private void serializeHelper(List<String> list, TreeNode node) {
        if (node == null) {
            return;
        }
        list.add(String.valueOf(node.val));
        serializeHelper(list, node.left);
        serializeHelper(list, node.right);
    }

    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        if (data == null || data.length() == 0) {
            return null;
        }
        // Queue<String> queue = new LinkedList(Arrays.asList(data.split(",")));
        // return deserializeHelper(queue, Integer.MIN_VALUE, Integer.MAX_VALUE);
        List<String> list = Arrays.asList(data.split(","));
        return deserializeHelper(list, new int[1], Integer.MIN_VALUE, Integer.MAX_VALUE);
    }

    // This helper function uses queue to construct the tree.
    private TreeNode deserializeHelper(Queue<String> queue, int min, int max) {
        if (queue == null || queue.isEmpty()) {
            return null;
        }
        int valToBeInserted = Integer.parseInt(queue.peek());
        if (valToBeInserted < min || valToBeInserted > max) {
            return null;
        }
        queue.poll();
        TreeNode node = new TreeNode(valToBeInserted);
        node.left = deserializeHelper(queue, min, valToBeInserted);
        node.right = deserializeHelper(queue, valToBeInserted, max);
        return node;
    }

    // This helper function uses list and index to construct the tree.
    private TreeNode deserializeHelper(List<String> list, int[] index, int min, int max) {
        if (index[0] == list.size()) {
            return null;
        }
        int valToBeInserted = Integer.parseInt(list.get(index[0]));
        if (valToBeInserted < min || valToBeInserted > max) {
            return null;
        }
        index[0]++;
        TreeNode node = new TreeNode(valToBeInserted);
        node.left = deserializeHelper(list, index, min, valToBeInserted);
        node.right = deserializeHelper(list, index, valToBeInserted, max);
        return node;
    }
}

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