Remove Duplicates from Sorted List

题目地址：https://leetcode.com/problems/remove-duplicates-from-sorted-list/

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.

题目要求去除一个有序的链表中的重复的元素，既然是有序的，那么重复元素肯定是相邻的，所以我们用两个相邻指针p和q（实际上，p.next=q），逐次向后遍历，发现重复的，则执行p = q.next，控制好停止状态即可。

public class RemoveDuplicatesFromSortedList {
    public ListNode deleteDuplicates(ListNode head) {
        if (head == null)
            return head;

        if (head.next == null)
            return head;

        ListNode p = head;
        ListNode q = head.next;

        while (q != null) {
            if (p.val == q.val) {
                p.next = q.next;
                q = p.next;
            } else {
                q = q.next;
                p = p.next;
            }
        }

        return head;
    }

    public static void main(String[] args) {
        ListNode node1 = new ListNode(3);
        ListNode node2 = new ListNode(3);
        ListNode node3 = new ListNode(3);
        ListNode node4 = new ListNode(3);
        ListNode node5 = new ListNode(3);
        ListNode node6 = new ListNode(3);

        node1.next = null;
        node2.next = node3;
        node3.next = node4;
        node4.next = node5;
        node5.next = node6;

        RemoveDuplicatesFromSortedList removeDuplicatesFromSortedList = new RemoveDuplicatesFromSortedList();
        removeDuplicatesFromSortedList.deleteDuplicates(node1);
    }
}

该实现时间复杂度为O(n)。