2 Add Two Numbers

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本文介绍了一种使用链表实现两个非负整数相加的方法。输入的两个链表以逆序方式存储数字，并返回结果作为新的链表。文章提供了一个Java实现示例，通过创建虚拟头节点简化了链表的处理。

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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.

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