LeetCode OJ：Insertion Sort List （插入排序链表）

Sort a linked list using insertion sort.

用插入排序来排序一个list，额， 我写的好麻烦啊， debug了好久，至少提交了5次。。。写吐了快，先贴代码，写的也好乱啊：

 class Solution {
 public:
     ListNode* insertionSortList(ListNode* hed) {
         if (hed == NULL) return NULL;
         head = hed;
         ListNode * insertPosPrev;
         ListNode * afterP;
         ListNode * prev = head;
         ListNode * p = head->next;
         while (p != NULL) {
             if (p->val > prev->val){
                 prev = p;
                 p = p->next;
                 continue;
             }
             insertPosPrev = findInsertPos(p);
             if (insertPosPrev == NULL) {//插入头节点之前
                 afterP = p->next;
                 prev->next = afterP;
                 p->next = head;
                 head = p;
                 p = afterP;
                 continue;
             }
             else if (p != insertPosPrev->next) {
                 afterP = p->next;
                 prev->next = afterP;
                 p->next = insertPosPrev->next;
                 insertPosPrev->next = p;
                 p = afterP;
                 continue;
             }
             prev = p;
             p = p->next;
         }
         return head;
     }

 private:
     ListNode * head;

     ListNode * findInsertPos(ListNode * end)
     {
         if (head->val >= end->val)
             return NULL;    //如果插入点在头节点那么返回NULL
         ListNode * prev = head;
         ListNode * p = prev->next;
         while (p != end) {
             if (prev->val < end->val && p->val >= end->val)
                 return prev;
             prev = p;
             p = p->next;
         }
         return prev;
     }
 };

这里贴一个大神的代码，有时间来看看，暂时还没看懂啊

 class Solution
 {
 public:
     ListNode *insertionSortList(ListNode *head)
     {
         if(head==NULL || head->next==NULL) return head;
         ListNode *cur=head;
         ListNode *helper=new ListNode();
         ListNode *pre;
         while(cur)
         {
             ListNode *next=cur->next;
             pre=helper;
             while(pre->next!=NULL && pre->next->val<cur->val)
             {
                 pre=pre->next;
             }
             cur->next=pre->next;
             pre->next=cur;
             cur=next;
         }
         return helper->next;
     }

 } ;

下面是java写的，第一遍写的基本上可以不看了，写的太麻烦了，下面这个写的稍微简单一点，代码如下：

 public class Solution {
     public ListNode insertionSortList(ListNode head) {
         if(head == null) return null;
         ListNode helper = new ListNode(Integer.MIN_VALUE);//将第一个节点的值设置成最小的
         helper.next = head;
         ListNode p = head.next;
         ListNode pPre = head;
         ListNode scan = helper;
         while(p != null){
             if(p.val >= pPre.val){
                 p= p.next;
                 pPre = pPre.next;
             }else{
                 while(p.val > scan.next.val){
                     scan = scan.next;
                 }
                 if(p.val >= scan.val && p.val <= scan.next.val){
                     ListNode tmp = scan.next;
                     scan.next = p;
                     pPre.next = p.next;
                     p.next = tmp;
                     p = pPre.next;
                     scan = helper; // 将扫描节点重新放置到链表的前部
                 }
             }
         }
         return helper.next;
     }
 }