173. 链表插入排序

173. 链表插入排序
 

用插入排序对链表排序
样例

样例 1:
    输入: 0->null
    输出: 0->null

样例 2:
    输入:  1->3->2->0->null
    输出 :0->1->2->3->null

 ListNode * insertionSortList(ListNode * head) {
        // write your code here
        
        if(NULL ==head)
        {
            return head;
        }
        
        ListNode * p= head;
        p=p->next;
        head->next=NULL;
        
        while(p)
        {
            ListNode * node = p;
            p=p->next;
            node->next = NULL;
          
            //在头部插入
            if(node->val <= head->val)
            {
                node->next = head;
                head=node;
            }
            else if(node->val>head->val)
            {
                cout<<"head->val"<<head->val<<endl;
                ListNode * tmp = head->next;
                ListNode * pre = head;
                while(tmp)
                {
                    if(tmp->val< node->val)
                    {
                        tmp=tmp->next;
                    }
                    else
                    {
                        break;
                    }
                    pre=pre->next;
                }
                cout<<"pre->val"<<pre->val<<endl;
                if(NULL == tmp) //在尾部插入
                {
                    pre->next = node;
                }
                else //在中部插入
                {
                    pre->next = node;
                    node->next=tmp;
                }
            }
        }
        
        return head;
        
    }