2. 两数相加

<?php
/**
 * Class ListNode
 * 链表
 */
Class ListNode {
    public $val = 0;
    public $next;
    public function __construct($val) {
        $this->val = $val;
    }
}
/**
 * (2->4->2)
 * +
 * (5->6->7)
 * =
 * (7->0->0->1)
 *
 */
Class Solution {
    public function addTwoNum(ListNode $n1, ListNode $n2) {
        $add = 0;
        $list = new ListNode(0);
        $cur = $list;
        while ($n1 || $n2) {
            $x = ($n1 != null) ? $n1->val : 0;
            $y = ($n2 != null) ? $n2->val : 0;
            $val = ($x + $y + $add) % 10;
            $add = floor(($x + $y + $add) / 10);
            $new = new ListNode($val);
            $cur->next = $new;
            $cur = $cur->next;
            if ($n1 != null) {
                $n1 = $n1->next;
            }
            if ($n2 != null) {
                $n2 = $n2->next;
            }
        }
        if ($add > 0) {
            $cur->next = new ListNode($add);
        }
        return $list->next;
    }
}
$n1 = new ListNode(2);
$n1->next = new ListNode(4);
$n1->next->next = new ListNode(2);
$n2 = new ListNode(5);
$n2->next = new ListNode(6);
$n2->next->next = new ListNode(7);
// 加
$cls = new Solution();
$ret = $cls->addTwoNum($n1, $n2);