LeetCode147. 对链表进行插入排序

我的代码：

 1 class Solution {
 2 public:
 3     ListNode* insertionSortList(ListNode* head) {
 4         if (!head || !head->next) return head;
 5         ListNode *res = head;
 6         ListNode *p1 = res;
 7         ListNode *pcur = head->next;
 8         ListNode *ppre = NULL; //已排序链表的ppre
 9         ListNode *pnext = NULL;
10         res->next = NULL;//先将链表断开，分为待插入和已排序两部分
11         while (pcur) {
12             pnext = pcur->next;
13             
14             ppre = NULL;
15             p1 = res;
16             while (p1 && p1->val < pcur->val) {
17                 ppre = p1;
18                 p1 = p1->next;
19             }
20             
21             //如果比已排序链表中所有元素都大，则尾插
22             if (p1 == NULL) {
23                 ppre->next = pcur;
24                 pcur->next = NULL;
25             }
26             //比已排序链表头结点都小，头插
27             else if (ppre == NULL) {
28                 pcur->next = res;
29                 res = pcur;
30             }
31             //如果在中间某处找到位置，则插入
32             else if (p1->val >= pcur->val) {
33                 pcur->next = p1;
34                 ppre->next = pcur;
35             }
36             
37             pcur = pnext;
38         }
39         return res;
40     }
41 };

LeetCode官方题解代码：

 1 class Solution {
 2 public:
 3     ListNode* insertionSortList(ListNode* head) {
 4         if (!head || !head->next) return head;
 5         ListNode *dummyHead = new ListNode(0);
 6         dummyHead->next = head;
 7         ListNode *lastSorted = head, *pcur = head->next;
 8         
 9         while (pcur) {
10             if (lastSorted->val <= pcur->val) {
11                 lastSorted = lastSorted->next;
12             }
13             else {
14                 ListNode *prev = dummyHead;
15                 while (prev->next->val <= pcur->val) {
16                     prev = prev->next;
17                 }
18                 lastSorted->next = pcur->next;
19                 //头插
20                 pcur->next = prev->next;
21                 prev->next = pcur;
22             }
23             pcur = lastSorted->next;
24         }
25         return dummyHead->next;
26     }
27 };

可以看出，我的代码有很多冗余的指针，且判断分支较多，不易读，官方代码就使用了三个指针，非常简洁。