leetcode 082 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.

Subscribe to see which companies asked this question

/**
 * 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 *l = head, *pre=head, *ret=NULL, *cur=NULL;

		if(head == NULL) return head;
		
		int cnt = 1;

		for(ListNode *next=l->next; next!=NULL; next=next->next) {
			if(pre->val == next->val) {
				cnt++;
				pre = next;
				continue;
			}

			if(cnt == 1)
			{
				if(ret == NULL) {
					ret = pre;
				}else {
					cur->next = pre;
				}
				cur = pre;
				cur->next=NULL;
				//cout << cur->val << endl;
			}

			cnt = 1;
			pre = next;
		}
        
        if(cnt == 1) {
            if(ret==NULL) {
                ret=pre;
            } else {
                cur->next=pre;
            }
            cur=pre;
            cur->next=NULL;
        }
		return ret;
    }
};