Remove Duplicates from Sorted List II

来源：Leetcode

原帖：http://oj.leetcode.com/problems/remove-duplicates-from-sorted-list-ii/

题目：
Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.
For example,
Given 1->2->3->3->4->4->5, return 1->2->5.
Given 1->1->1->2->3, return 2->3.

代码：
1] iteration

 /**  
  * Definition for singly-linked list.  
  * struct ListNode {  
  *   int val;  
  *   ListNode *next;  
  *   ListNode(int x) : val(x), next(NULL) {}  
  * };  
  */  
 class Solution {  
 public:    
     ListNode *deleteDuplicates(ListNode *head) {  
         if (!head || !head->next) return head;      
         ListNode dummy(0);  
         dummy.next = head;  
         head = &dummy;   
         while (head->next && head->next->next) {  
             if (head->next->val == head->next->next->val) {  
                 int val = head->next->val;  
                 while (head->next && head->next->val == val) {  
                     ListNode* node = head->next;  
                     head->next = head->next->next;  
                     delete node;  
                 }        
             } else {  
                 head = head->next;  
             }  
         }  
         return dummy.next;  
     }  
 };  

2] recursion

 class Solution {  
 public:  
     ListNode *deleteDuplicates(ListNode *head) {  
         if (!head) {  
             return NULL;  
         }  
         if (!head->next || head->val != head->next->val) {  
             head->next = deleteDuplicates(head->next);  
             return head;  
         }  
         int val = head->val;  
         while (head && head->val == val) {  
             ListNode *temp = head;  
             head = head->next;  
             delete temp;  
         }      
         return deleteDuplicates(head);  
     }  
 };