[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;    }};