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

.
原题链接：https://oj.leetcode.com/problems/remove-duplicates-from-sorted-list-ii/
题目：给定一个已排序的链表，删除重复的元素，只留下源链表中唯一出现的那些元素。

思路：首先防止把头节点删除，构建一个虚拟的头节点。由于是已排序的，相等的元素就在相邻的位置上，发现有相邻的元素，则指针依次向后指，直到没有相等的相邻元素为止。

public ListNode deleteDuplicates(ListNode head) {
if (head == null || head.next == null)
return head;

ListNode dummy = new ListNode(0);
dummy.next = head;
head = dummy;

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

return dummy.next;
}

// Definition for singly-linked list.
public class ListNode {
int val;
ListNode next;

ListNode(int x) {
val = x;
next = null;
}
}