83. Remove Duplicates from Sorted List

题目：

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

.

链接： http://leetcode.com/problems/remove-duplicates-from-sorted-list/

一刷，在考虑什么时候应该使用dummy node，什么时候不应该。感觉跟第一个元素有关，如果第一个元素肯定在输出中，可以不使用dummy node。

class Solution(object):
def deleteDuplicates(self, head):
"""
:type head: ListNode
:rtype: ListNode
"""
if not head:
return head
prev = head
current = head.next

while current:
if prev.val == current.val:
prev.next = current.next
else:
prev = prev.next
current = current.next
return head

2/14/2017, Java

/**
* Definition for singly-linked list.
* public class ListNode {
*     int val;
*     ListNode next;
*     ListNode(int x) { val = x; }
* }
*/
public class Solution {
public ListNode deleteDuplicates(ListNode head) {
if (head == null) return null;
ListNode current = head;

while (current != null) {
if (current.next != null && current.next.val == current.val) current.next = current.next.next;
else current = current.next;
}
return head;
}
}