[LeetCode] Problem 2 - Add Two Numbers

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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 contain a single digit. Add the two numbers and return it as a linked list.

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

Example

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)

Output: 7 -> 0 -> 8

Explanation: 342 + 465 = 807.

Code

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public class ListNode {
    int val;
    ListNode next;
    ListNode(int x) { val = x; }
}
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public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
    ListNode head = new ListNode(0);
    ListNode current1 = l1;
    ListNode current2 = l2;
    ListNode current = head;
    int carry = 0;

    while (current1 != null || current2 != null) {
        int val1 = current1 == null ? 0 : current1.val;
        int val2 = current2 == null ? 0 : current2.val;
        int sum = val1 + val2 + carry;

        current.next = new ListNode(sum % 10);
        carry = sum / 10;

        current = current.next;

        if (current1 != null)
            current1 = current1.next;

        if (current2 != null)
            current2 = current2.next;
    }

    if (carry > 0)
        current.next = new ListNode(carry);

    return head.next;
}