《leetCode-php》去掉有序連結清單中重複的值

給出一個排好序的連結清單，删除連結清單中的所有重複出現的元素，隻保留原連結清單中隻出現一次的元素。 

例如： 

給出的連結清單為1->2->3->3->4->4->5, 傳回1->2->5.

給出的連結清單為1->1->1->2->3,  傳回2->3.

思路：這個主要是頭結點怎麼處理

<?php
class Node {
    public $next = null;
    public $val;
    public function __construct($val) {
        $this->val = $val;
    }
}
function deleteDuplicates($head) {
    //先要找一個新的頭節點,友善找到下一個頭結點
    $newHead = new Node($head->val - 1);
    $newHead->next = $head;
    $node = $newHead;
    $pre = $newHead;//用來記錄前一個節點
    while ($node != null) {
        if ($node->val == $node->next->val) {
            $node1 = $node->next;
            while ( $node1 != null && $node1->val == $node->val) {
                $node1 = $node1->next;
            }
            $pre->next = $node1;
            $node = $node1;
            continue;
        }
        $pre = $node;
        $node = $node->next;
    }
    return $newHead->next;
}
$node1 = new Node(1);
$node2 = new Node(2);
$node3 = new Node(2);
$node4 = new Node(2);
$node5 = new Node(3);
$node6 = new Node(3);
$node7 = new Node(4);
$node1->next = $node2;
$node2->next = $node3;
$node3->next = $node4;
$node4->next = $node5;
$node5->next = $node6;
$node6->next = $node7;
$ret = deleteDuplicates($node1);
while ($ret != null) {
    print $ret->val . "\n";
    $ret = $ret->next;
}