56_leetcode_Remove Duplicates from Sorted Lists 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.

1:特殊情况，空链表和只有一个节点；2:设置startNode和endNode两个节点；当两个节点的val值不等的时候，若两者前后，则startNode只有一个，进行处理；若两者不前后，则说明两者中间右多余的节点；3:最后考虑startNode的情况以及根据index的值来处理next指针。

    ListNode *deleteDuplicates(ListNode *head)    {        if(head == NULL || head->next == NULL)        {            return head;        }                ListNode* newHead = NULL;        ListNode* index = NULL;        ListNode* startNode = head;        ListNode* endNode = head->next;                while(endNode)        {            if(endNode->val == startNode->val)            {                endNode = endNode->next;            }            else            {                if(startNode->next == endNode)                {                    if(newHead == NULL)                    {                        newHead = startNode;                        index = startNode;                    }                    else                    {                        index->next = startNode;                        index = index->next;                    }                }                startNode = endNode;                endNode = endNode->next;            }        }                if(startNode->next == NULL)        {            if(newHead == NULL)            {                newHead = startNode;            }            else            {                index->next = startNode;                index = index->next;            }        }        else        {            if(index)            {                index->next = NULL;            }        }                return newHead;            }