Utils.java

package com.freetymekiyan.algorithms.utils;

import java.security.InvalidParameterException;
import java.util.ArrayDeque;
import java.util.Queue;

/**
 * Utility class.
 */
public class Utils {

    public static ListNode buildLinkedList(int[] values) {
        ListNode head = new ListNode(values[0]);
        ListNode cur = head;
        for (int i = 1; i < values.length; i++) {
            cur.next = new ListNode(values[i]);
            cur = cur.next;
        }
        return head;
    }

    public static TreeNode buildBinaryTree(Integer[] values) {
        if (values == null || values.length == 0) {
            throw new InvalidParameterException("values should not be null or empty");
        }
        TreeNode root = new TreeNode(values[0]);
        Queue<TreeNode> queue = new ArrayDeque<>();
        queue.offer(root);
        int i = 1;
        while (!queue.isEmpty() && i < values.length) {
            TreeNode node = queue.poll();
            if (i < values.length && values[i] != null) {
                node.left = new TreeNode(values[i]);
                queue.offer(node.left);
            }
            if (i + 1 < values.length && values[i + 1] != null) {
                node.right = new TreeNode(values[i + 1]);
                queue.offer(node.right);
            }
            i += 2;
        }
        return root;
    }

    public static class ListNode {

        public int val;
        public ListNode next;

        public ListNode(int x) {
            val = x;
        }
    }

    public static class TreeNode {

        public int val;
        public TreeNode left;
        public TreeNode right;

        public TreeNode(int x) {
            val = x;
        }
    }
}