[LeetCode] 82. Remove Duplicates from Sorted List II

Problem : https://leetcode.com/problems/remove-duplicates-from-sorted-list-ii/

Traverse the origin linked list and count the visited numbers.  Then append distinct number to the output linked list.

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def deleteDuplicates(self, head: ListNode) -> ListNode:
        
        dummy = ListNode(0)
        p1 = dummy
        
        p2 = head
        count = 1
        
        while p2 and p2.next:
            if p2.val == p2.next.val:
                count += 1
                p2 = p2.next
            else:
                if count == 1:
                    p1.next = p2
                    p1 = p1.next
                
                count = 1
                p2 = p2.next
    
        if p2 and count == 1:
            p1.next = p2
            p1 = p1.next
        
        # end the output linked list
        p1.next = None
        
        return dummy.next

A Sliding-window solution:

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def deleteDuplicates(self, head: ListNode) -> ListNode:
        p = head
        q = head
        
        dummy = ListNode()
        n = dummy
        
        while p:
            while q and p.val == q.val:
                q = q.next
            
            if p.next == q:
                n.next = p
                n = n.next
            
            p = q
            
        # end the new list
        n.next = None
            
        return dummy.next