【LeetCode】-Remove Duplicates from Sorted List II

Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.

For example,

Given 

1->2->3->3->4->4->5

, return 

1->2->5

.

Given 

1->1->1->2->3

, return 

2->3

.

/**
* 解题思路：
* 保留与前后节点val不同的节点
*
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) {
* val = x;
* next = null;
* }
* }
*/
public class Solution {
public ListNode deleteDuplicates(ListNode head) {
if(head==null)
return null;
if(head.next==null)
return head;
ListNode newHead = new ListNode(0);
ListNode tail = newHead;
if( head.next!=null && head.val!=head.next.val ){
tail.next = head;
tail = tail.next;
}

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