1. 概述

给定一个排序链表，删除所有重复的元素，使得每个元素只出现一次。
示例 1: 输入: 1->1->2

输出: 1->2

示例 2:

输入: 1->1->2->3->3

输出: 1->2->3

2. 解题

<?php
class ListNode {
    /** @var int */
    public $val = 0;
    /** @var ListNode */
    public $next = null;
    function __construct($val) { $this->val = $val; }
}
class Solution {
    /**
     * @param ListNode $head
     * @return ListNode
     */
    public function deleteDuplicates($head) {
        $p = $head;
        $checkVal = $head->val;
        while ($p->next) {
            if ($p->next->val == $checkVal && $p->next->next) {
                $p->next = $p->next->next;
            } else {
                $checkVal = $p->next->val;
                $p = $p->next;
            }
        }
        return $head;
    }
}
$head = new ListNode(1);
$head->next = new ListNode(1);
$head->next->next = new ListNode(2);
$head->next->next->next = new ListNode(3);
$head->next->next->next->next = new ListNode(4);
$cls = new Solution();
$ret = $cls->deleteDuplicates($head);
print_r($ret);