题解 | #链表的插入排序#

import java.util.*;

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

public class Solution {
    /**
     * 
     * @param head ListNode类 
     * @return ListNode类
     */
    public ListNode insertionSortList (ListNode head) {
        // write code here
        if(head==null||head.next==null)    return head;

        ListNode pre = head;//pre指向已经有序的节点
        ListNode cur = head.next;//cur指向待排序的节点

        ListNode aux = new ListNode(-1);//辅助节点
        aux.next = head;

        while(cur!=null){
            if(cur.val<pre.val){
                //先把cur节点从当前链表中删除，然后再把cur节点插入到合适位置
                pre.next = cur.next;

                //从前往后找到l2.val>cur.val,然后把cur节点插入到l1和l2之间
                ListNode l1 = aux;
                ListNode l2 = aux.next;
                while(cur.val>l2.val){
                    l1 = l2;
                    l2 = l2.next;
                }
                //把cur节点插入到l1和l2之间
                l1.next = cur;
                cur.next = l2;//插入合适位置

                cur = pre.next;//指向下一个待处理节点

            }else{
                pre = cur;
                cur = cur.next;
            }
        }
        return aux.next;
    }

}