[LeetCode] Remove Duplicates from Sorted List II

Remove Duplicates from Sorted List II

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

.
解题思路：

这道题的题意是删除有序链表中所有出现两次或两次以上的元素。本身没有较大的难度，注意第一个元素可能是重复元素的情况。

/**
* 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) {
ListNode* myHead=new ListNode(0);
ListNode* tail = myHead->next;
ListNode* preTail = myHead;
ListNode* p = head, *q;
while(p!=NULL){
if(tail==NULL){
tail = p;
preTail->next = tail;
p=p->next;
tail->next = NULL;
}else if(tail->val != p->val){
tail->next = p;
p=p->next;
tail = tail->next;
tail->next = NULL;
preTail = preTail->next;
}else{
while(p!=NULL && tail->val == p->val){
q = p;
p=p->next;
delete q;
}
delete tail;
tail = NULL;
preTail->next=NULL;
}
}
p=myHead;
myHead = myHead->next;
delete p;
return myHead;
}
};