# 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.
Example:
Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.
# Solution
Approach 1: Elementary math.
# Code (Python)
Approach 1:
# Code (C++)
Approach 1:
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
ListNode *head = NULL;
ListNode *tail = NULL;
ListNode *p1 = l1;
ListNode *p2 = l2;
int sum = 0;
while (p1 != NULL || p2 != NULL)
{
if (p1 != NULL) sum += p1->val;
if (p2 != NULL) sum += p2->val;
if (head == NULL && tail == NULL)
{
tail = new ListNode(sum % 10);
head = tail;
}
else
{
tail->next = new ListNode(sum % 10);
tail = tail->next;
}
sum = sum / 10;
if (p1 != NULL) p1 = p1->next;
if (p2 != NULL) p2 = p2->next;
}
if (sum > 0)
{
tail->next = new ListNode(sum);
tail = tail->next;
}
return head;
}
};