---
tags: Leetcode
---
# 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.

Example:

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

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*Figure 1. Visualization of the addition of two numbers: 342 + 465 = 807342+465=807.
Each node contains a single digit and the digits are stored in reverse order*.

:::warning
注意 :zap: 這裡的 ListNode 為自訂 Linked list，可以學一下
:::

---

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