2. Add Two Numbers

2. Add Two Numbers

Medium

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order, and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Example 1:

• Input: l1 = [2,4,3], l2 = [5,6,4]
• Output: [7,0,8]
• Explanation: 342 + 465 = 807.

Example 2:

• Input: l1 = [0], l2 = [0]
• Output: [0]

Example 3:

• Input: l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9]
• Output: [8,9,9,9,0,0,0,1]

Constraints:

• The number of nodes in each linked list is in the range [1, 100].
• 0 <= Node.val <= 9
• It is guaranteed that the list represents a number that does not have leading zeros.

Solution:

/**
 * Definition for a singly-linked list.
 * class ListNode {
 *     public $val = 0;
 *     public $next = null;
 *     function __construct($val = 0, $next = null) {
 *         $this->val = $val;
 *         $this->next = $next;
 *     }
 * }
 */
class Solution {

    /**
     * @param ListNode $l1
     * @param ListNode $l2
     * @return ListNode
     */
    function addTwoNumbers($l1, $l2) {
        $dummyHead = new ListNode(0);
        $p = $l1;
        $q = $l2;
        $curr = $dummyHead;
        $carry = 0;

        while ($p !== null || $q !== null) {
            $x = ($p !== null) ? $p->val : 0;
            $y = ($q !== null) ? $q->val : 0;
            $sum = $carry + $x + $y;
            $carry = (int)($sum / 10);

            $curr->next = new ListNode($sum % 10);
            $curr = $curr->next;

            if ($p !== null) {
                $p = $p->next;
            }
            if ($q !== null) {
                $q = $q->next;
            }
        }

        if ($carry > 0) {
            $curr->next = new ListNode($carry);
        }

        return $dummyHead->next;
    }
}

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