LeetCode: Merge Two Sorted Lists

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

public class MergeTwoSortedLists {
  public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
    // leetcode supports lambda
    Queue<ListNode> queue = new PriorityQueue<>(2, (o1, o2) -> o1.val - o2.val);

    if (l1 != null) queue.add(l1);
    if (l2 != null) queue.add(l2);

    ListNode pre, cursor;
    pre = new ListNode(0);
    cursor = pre;
    while (!queue.isEmpty()) {
      ListNode node = queue.poll();
      cursor.next = node;
      cursor = cursor.next;
      if (node.next != null) {
        queue.add(node.next);
      }
    }
    return pre.next;
  }
}