链表的排序 ---链表插入排序

/**
 * 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 * dummy = new ListNode(-1);
          dummy->next = head;   
          
          ListNode * pre = head ;
          ListNode * cur = head->next ; // 从第二个节点开始
          
          while(cur)
          {
              if(pre->val > cur->val)  // 这里假设从 头节点到 pre 节点 之间 是排好序的
              {
                  ListNode *tmp = dummy;
                  while(tmp->next->val<cur->val)
                     tmp= tmp->next;
                    
                    pre->next = cur->next;   // 将pre 与cur 后面的节点连接
                    cur->next = tmp->next;   // cur 插入适当的位置
                    tmp->next = cur;
                     
              }
              else 
                 pre = pre->next ;   
                 
                 cur = pre->next;
          }
          
          return dummy->next;
          
    }
};