题解 | #单链表的排序#

堆排序应该是最简单直观的，且时间复杂度和空间复杂度都符合题目要求。注意点就是最后一个节点的next指针要设置为null，否则可能会出现环形链表的情况

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 * }
 */

public class Solution {
    /**
     * 
     * @param head ListNode类 the head node
     * @return ListNode类
     */
    public ListNode sortInList (ListNode head) {
        // write code here
        PriorityQueue<ListNode> heap = new PriorityQueue<>((n1, n2) -> n1.val - n2.val);
        while (head != null) {
            heap.add(head);
            head = head.next;
        }
        ListNode dummy = new ListNode(-1);
        ListNode cur = dummy;
        while (!heap.isEmpty()) {
            cur.next = heap.poll();
            cur = cur.next;
        }
        cur.next = null;
        return dummy.next;
    }
}