Add Two Numbers

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

/**
* Definition for singly-linked list.
* public class ListNode {
*     int val;
*     ListNode next;
*     ListNode(int x) { val = x; }
* }
*/
public class Solution {
public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
ListNode root = new ListNode(0);
ListNode l1Index = l1, l2Index = l2, rLast = root;
int sum = 0;
while(l1Index != null || l2Index != null){
if(l1Index != null){
sum += l1Index.val;
l1Index = l1Index.next;
}
if(l2Index != null){
sum += l2Index.val;
l2Index = l2Index.next;
}
rLast.val = sum % 10;
sum /= 10;  // 记录sum的值
if(l1Index != null || l2Index != null){
rLast.next = new ListNode(0);
rLast = rLast.next;
}
}
if(sum != 0){
rLast.next = new ListNode(sum);
}
return root;
}
}