297. Serialize and Deserialize Binary Tree

/**
 * 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 "#";
        }
        StringBuilder sb = new StringBuilder();
        serializeHelper(sb, root);
        System.out.println(sb.toString());
        return sb.toString();
    }

    private void serializeHelper(StringBuilder sb, TreeNode node) {
        if (node == null) {
            sb.append("#");
            return;
        }
        sb.append(node.val).append(",");
        serializeHelper(sb, node.left);
        sb.append(",");
        serializeHelper(sb, node.right);
    }

    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        if (data == null || data.length() == 0) {
            return null;
        }
        return deserializeHelper(new LinkedList<String>(Arrays.asList(data.split(","))));
    }

    private TreeNode deserializeHelper(Queue<String> queue) {
        if (queue.isEmpty()) {
            return null;
        }
        String valToBeAdded = queue.poll();
        if ("#".equals(valToBeAdded) || valToBeAdded.length() == 0) {
            return null;
        }
        TreeNode node = new TreeNode(Integer.parseInt(valToBeAdded));
        node.left = deserializeHelper(queue);
        node.right = deserializeHelper(queue);
        return node;
    }
}

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