AddTwoNumbers.java

/*
 Author:     King, wangjingui@outlook.com
 Date:       Dec 13, 2014
 Problem:    Add Two Numbers
 Difficulty: easy
 Source:     https://oj.leetcode.com/problems/add-two-numbers/
 Notes:
 You are given two linked lists representing two non-negative numbers. 
 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.

 Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
 Output: 7 -> 0 -> 8

 Solution: dummy head...

 */
/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode dummy = new ListNode(0);
        ListNode cur = dummy;
        int carry = 0;
        while (l1 != null || l2 != null || carry != 0) {
            int sum = carry;
            if (l1 != null) {
                sum += l1.val;
                l1 = l1.next;
            }
            if (l2 != null) {
                sum += l2.val;
                l2 = l2.next;
            }
            carry = sum/10;
            sum = sum%10;
            ListNode node = new ListNode(sum);
            cur.next = node;
            cur = cur.next;
        }
        return dummy.next;
    }
}