Add Two Numbers

题目描述

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.

Example

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.

对两个链表求和，链表的低位对应数字的低位。

解题思路

用一个 carry 存储进位，一直加到 l1，l2 为 null，且 carry 为 0 时，运算完成。

代码

class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        if (l1 == null || l2 == null)
            return null;
        ListNode first = new ListNode(-1);
        ListNode node = first;
        int carry = 0;
        while (l1 != null || l2 != null || carry != 0) {
            int a = 0;
            int b = 0;
            if (l1 != null) {
                a = l1.val;
                l1 = l1.next;
            }
            if (l2 != null) {
                b = l2.val;
                l2 = l2.next;
            }
            node.next = new ListNode((a+b+carry)%10);
            node = node.next;
            carry = (a+b+carry) / 10;
        }
        return first.next;
    }
}