[leedcode 147] Insertion Sort List

Sort a linked list using insertion sort.

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    //插入排序，时间复杂度O(n^2),注意终止条件，默认p之前的已经从小到大排好序了
    public ListNode insertionSortList(ListNode head) {
        if(head==null||head.next==null) return head;
        ListNode newHead=new ListNode(-1);
        newHead.next=head;
        ListNode p=head.next;
        ListNode ppre=head;
        boolean flag=false;
        while(p!=null){///
          if(p.val>ppre.val){//
              p=p.next;
              ppre=ppre.next;
          }else{
              ListNode q=newHead.next;
              ListNode qpre=newHead;
              while(q.val<p.val){
                  qpre=qpre.next;
                  q=q.next;
              }
              ppre.next=p.next;
              qpre.next=p;
              p.next=q;
              p=ppre.next;
              
          }
        }
        return newHead.next;
    }
}