83. Remove Duplicates from Sorted List
Given a sorted linked list, delete all duplicates such that each element appear only once.
思路同删除排序数组中的重复元素。使用一个指针指向目标链表的末尾，遍历原链表，如果原链表元素与目标链表尾元素不同，则把该元素添加到目标链表末尾。
# Definition for singly-linked list.
class ListNode:
def __init__(self, x):
self.val = x
self.next = None
class Solution:
def deleteDuplicates(self, head: ListNode) -> ListNode:
if not head:
return head
index, next_ = head, head.next
while next_:
if next_.val != index.val:
index.next = next_
index = index.next
next_ = next_.next
index.next = None
return head