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

Example 1:

Input: 1->1->2
Output: 1->2
Example 2:

Input: 1->1->2->3->3
Output: 1->2->3
"""

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

class Solution:
    def deleteDuplicates(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        value = dict()
        cur = head
        pre = None

        while cur:
            if cur.val not in value:
                value[cur.val] = None
                pre = cur
                cur = cur.next
            else:
                pre.next = cur.next
                cur = cur.next
        return head