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leetcode – Add Two Numbers

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 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.

Solution

/**
 * Definition for singly-linked list.
 * public class ListNode {
 * int val;
 * ListNode next;
 * ListNode(int x) { val = x; }
 * }
 */
public class Question2Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {

        ListNode head = new ListNode(0);

        int carry = 0;

        ListNode currNode = head ;

        while (l1 != null || l2 != null) {
            int x1 = (l1 != null ? l1.val : 0);
            int x2 = (l2 != null ? l2.val : 0);

            int sum = x1 + x2 + carry;
            carry = sum / 10;
            currNode.next = new ListNode(sum % 10);
            currNode = currNode.next;

            if (l1 != null) l1 = l1.next;
            if (l2 != null) l2 = l2.next;

        }

        if (carry == 1) {
            currNode.next = new ListNode(carry);
        }
        return head.next;

    }

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