思路：创建一辅助节点，作为生成链表的头结点（不含有效数据）。遍历原链表中每一个节点，并将其插入到新链表的对应位置
/**
* 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) {
ListNode *dump = new ListNode(0);
if(head == NULL || head->next == NULL)
return head;
ListNode *prev = dump;
ListNode *cur = head;
ListNode *tmp;
while(cur)
{
prev = dump;
while((prev->next != NULL)&&(prev->next->val < cur->val))//找到一点，在该点之后插入
prev= prev->next;
tmp = cur->next;
cur->next = prev->next;
prev->next = cur;
cur = tmp;
}
return dump->next;
}
};