#python3
'''
Given a sorted linked list, delete all duplicates such that each element appear only once.

For example,
Given 1->1->2, return 1->2.
Given 1->1->2->3->3, return 1->2->3.
'''
# 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
        """
		previous = ListNode(None)
		current = head
        while current:
			
			if current.val == previous.val:
				previous.next = current.next
			else:
				previous = current
				
			
			current = current.next