leetcode:Insertion Sort List

/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode *insertionSortList(ListNode *head) {
if(head==NULL || head->next==NULL) return head;

ListNode *pre;
ListNode *p=head;
ListNode *ph=head;
ListNode *pcur=head->next;
p->next=NULL;
ListNode *pnext=NULL;

while(pcur!=NULL)
{
pnext=pcur->next;
while(p!=NULL && p->val<=pcur->val)
{
pre=p;
p=p->next;
}
if(p==ph)
{
pcur->next=p;
ph=pcur;
}

else if(pre->next==NULL)           //如果是else if(p==NULL)的话，条件判断语句好像不能判断该句，导致结果错误
{
pre->next=pcur;
pcur->next=NULL;
}

else
{
pre->next=pcur;
pcur->next=p;
}

pcur=pnext;
p=ph;
}
return ph;
}
};