83.Remove Duplicates from Sorted List

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
        """
        if head==None:
            return head
        first,second = head,head.next
        while second:
            if first.val == second.val:
                first.next = second.next
                second = second.next
            else:
                first = first.next
                second = second.next
        return head