2. 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 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.

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

Solution:

Tips:

pay attention to the last carry bit and graceful code.

Java Code:

/** * 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) {        // add a new node for header, will omit some if ... else ... statements        ListNode resultList = new ListNode(0);        ListNode tmpNode = resultList;        int carry = 0;                while (l1 != null || l2 != null || carry != 0) {            int currentVal = 0;            if (l1 != null && l2 != null) {                currentVal = l1.val + l2.val + carry;                l1 = l1.next;                l2 = l2.next;            } else if (l1 != null) {                currentVal = l1.val + carry;                l1 = l1.next;            } else if (l2 != null) {                currentVal = l2.val + carry;                l2 = l2.next;            } else {                currentVal = carry;            }            carry = currentVal / 10;            currentVal %= 10;            ListNode node = new ListNode(currentVal);            tmpNode.next = node;            tmpNode = node;        }                return resultList.next;    }}