Leetcode #2. Add Two Numbers

 Leetcode #2. Add Two Numbers

 ◎ 難度： Medium

 ◎ 題目：

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 contains a single digit. 
Add the two numbers and return the sum as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.


給你兩個 非空白的非負數(可能會有0)的linked lists，以降暮排序
每個節點都有一個0~9的個位數字
將每個節點數字分別加總後，以linked lists返回
返回的各節點值，僅限個位數字，進位數字加總到下一節點(需特別處理進位問題) 




 ◎ Example 1:

Input: l1 = [2,4,3], l2 = [5,6,4]
Output: [7,0,8]
Explanation: 342 + 465 = 807.
*** 第二個節點相加 (4+6=10)，個位數為 0， 十位數字 加總到下一節點
所以，節點三 = 3+4+1(第二節點進位) = 8

 ◎ Example 2:

Input: l1 = [0], l2 = [0]
Output: [0]

 ◎ Example 3:

Input: l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9]
Output: [8,9,9,9,0,0,0,1]

 ◎ Constraints:
The number of nodes in each linked list is in the range [1, 100].
0 <= Node.val <= 9
It is guaranteed that the list represents a number that does not have leading zeros.




 ◎ 想法：
每個節點的值 最大=9
9+9=18，最大進位數字 =1
我們僅需要紀錄，前一節點加總後 是否有進位；有的話 這節點需 +1 
再來須注意 輸入的兩個節點長度，可能是不相同的
然後，各節點取個位數字返回即可


 ◎ C++程式碼：

Leetcode #1 - Two Sum

 Leetcode #1 - Two Sum

 ◎ 難度： Easy

 ◎ 題目：

Given an array of integers nums and an integer target, return