Sort a linked list using insertion sort.

指针的初始值设置有问题，梁旭两天童颜的错误了。

/** * 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 * guide = new ListNode(0);        guide->next = head;        ListNode * temp = head->next;        ListNode * temp_pre = head;        while(temp != NULL)        {            int temp_val = temp->val;            ListNode * p = guide->next;            ListNode * p_pre = guide;            while(temp_val > p->val && p != temp)            {                p = p->next;                p_pre =p_pre->next;            }            if(p == temp)            {                temp =temp->next;                temp_pre = temp_pre->next;                continue;            }            else            {                temp_pre ->next =temp->next;                p_pre->next =temp;                temp->next = p;                temp = temp_pre->next;                //return guide->next;            }                    }        return guide->next;            }};