82. Remove Duplicates from Sorted List II

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problem:

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.

多指针循环判断即可，注意特殊情况

class Solution {public:    ListNode* deleteDuplicates(ListNode* head) {        ListNode* result = new ListNode(0);        if(head == NULL || head->next == NULL)            return head;        int flag = 0;        int last;        ListNode* index = head;        ListNode* resultindex = new ListNode(0);        if(head->val != head->next->val)        {            result->next = index;            last = index->val;            index = index->next;            result->next->next = NULL;            resultindex = result->next;            flag++;        }        else            last = index->val;        while(index != NULL)        {            if(index->val != last)            {                ListNode* nextnode = index->next;                if(nextnode != NULL && index->val == nextnode->val)                {                    last = index->val;                    index = index->next;                }                else                {                    if(flag == 0)                    {                        result->next = index;                        index = index->next;                        if(index != NULL)                            result->next->next = NULL;                        resultindex = result->next;                        flag++;                    }                    else                    {                        last = index->val;                        resultindex->next = index;                        index = index->next;                        resultindex = resultindex->next;                        resultindex->next = NULL;                    }                }            }            else            {                index = index->next;            }        }        return result->next;    }};

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