0002. Add Two Numbers

https://leetcode.com/problems/add-two-numbers

Description

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.

ac

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode dummy = new ListNode(0);
        ListNode head = dummy;

        int carry = 0;
        while (l1 != null || l2 != null) {
            int curr = carry;
            curr += l1 != null ? l1.val : 0;
            curr += l2 != null ? l2.val : 0;
            carry = curr / 10;

            ListNode tmp = new ListNode(curr % 10);
            head.next = tmp;
            head = head.next;

            if (l1 != null) l1 = l1.next;
            if (l2 != null) l2 = l2.next;
        }
        // last one
        if (carry > 0) head.next = new ListNode(carry);

        return dummy.next;
    }
}