PU Remove Duplicates from Sorted List II

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */
struct ListNode* deleteDuplicates(struct ListNode* head) {
    struct ListNode dummy, *p = &dummy;
    p->next = head;
    struct ListNode *l = head, *r;
    while (l) {
        r = l->next;
        while (r && r->val == l->val) r = r->next;
        if (r != l->next) p->next = r;
        else p = l;
        l = r;
    }
    return dummy.next;
}

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def deleteDuplicates(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        if not head or not head.next: return head
        dummy = ListNode(0)
        dummy.next = head
        cur, r, rr = dummy, head, head.next
        while r and rr:
            if r.val != rr.val:
                cur, r, rr = r, rr, rr.next
                continue
            val = r.val
            while cur.next:
                if cur.next.val != val: break
                cur.next = cur.next.next
            if not cur.next: break
            r, rr = cur.next, cur.next.next
        return dummy.next

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def deleteDuplicates(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        if not head or not head.next: return head
        dummy = ListNode(0)
        dummy.next = head
        cur, r = dummy, head
        while r:
            rr = r.next
            while rr and rr.val == r.val:
                rr = rr.next
            if rr != r.next: 
                cur.next = r = rr
            else: 
                cur, r = r, rr
        return dummy.next