LeetCode 82. Remove Duplicates from Sorted List II

/** * 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 *s = head,*e = head;        while(head&&head->next&&head->val == head->next->val)        {            e = head->next;            int val = e->val;            while(e&&e->val == val)                e = e->next;            head = e;        }        if(head == NULL) return NULL;        if(head->next== NULL) return head;                s = head;        while(s->next&&s->next->next)        {            if(s->next->val != s->next->next->val)                s = s->next;            else            {                e = s->next;                int val = e->val;                while(e&&e->val == val)                    e=e->next;                s->next = e;            }        }        return head;    }};