LeetCode Insertion Sort List

Sort a linked list using insertion sort.

题目意思是用插入排序对单链表进行排序，做法是返回一个新的单链表，每次插入的时候都添加一个新建的节点。

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode insertionSortList(ListNode head) {
       if (head==null || head.next==null) {
        return head;
       }
       ListNode first = new ListNode(head.val);
       ListNode curr = head.next;
       ListNode last = first,temp=first;
       
       while (curr!=null) {
        if (curr.val>=last.val) {
            ListNode newlast = new ListNode(curr.val);
            last.next=newlast;
            last=newlast;
        }else {
            if (first.val>=curr.val) {
                ListNode newfirst=new ListNode(curr.val);
                newfirst.next=first;
                first=newfirst;
            }else {
                temp=first;
                while (curr.val>temp.val&&curr.val>temp.next.val) {
                    temp=temp.next;
                }
                ListNode newmiddle = new ListNode(curr.val);
                newmiddle.next=temp.next;
                temp.next=newmiddle;
            }
        }    
        curr=curr.next;
    }
       return first;
    }
}