题目描述：
    image.png
    解析：优先级队列

    1. class Solution {
    2.     public ListNode sortList(ListNode head) {
    3.         ListNode dummy = new ListNode(0);
    4.         ListNode curr = dummy;
    5.         PriorityQueue<ListNode> priorityQueue = new PriorityQueue<>((o1, o2) -> o1.val-o2.val);
    6.         while (head != null) {
    7.             priorityQueue.offer(new ListNode(head.val));
    8.             head = head.next;
    9.         }
    10.         while (!priorityQueue.isEmpty()) {
    11.             curr.next = priorityQueue.poll();
    12.             curr=curr.next;
    13.         }
    14.         return dummy.next;
    15.     }
    16. }