# Add Two Numbers II Problem

## Description

LeetCode Problem 445.

You are given two non-empty linked lists representing two non-negative integers. The most significant digit comes first 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.

Example 1:

``````1
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Input: l1 = [7,2,4,3], l2 = [5,6,4]
Output: [7,8,0,7]
``````

Example 2:

``````1
2
Input: l1 = [2,4,3], l2 = [5,6,4]
Output: [8,0,7]
``````

Example 3:

``````1
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Input: l1 = , l2 = 
Output: 
``````

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.

## Sample C++ Code

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/**
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode() : val(0), next(nullptr) {}
*     ListNode(int x) : val(x), next(nullptr) {}
*     ListNode(int x, ListNode *next) : val(x), next(next) {}
* };
*/
class Solution {
public:
ListNode* addTwoNumbers(ListNode* h1, ListNode* h2) {
stack<int> s1, s2;
while (h1) {
s1.push(h1->val);
h1 = h1->next;
}
while (h2) {
s2.push(h2->val);
h2 = h2->next;
}
int carry_on = 0;
ListNode *curr = NULL, *prev = NULL;
while (s1.size() || s2.size() || carry_on) {
int sum = carry_on;
if (s1.size()) {
sum += s1.top();
s1.pop();
}
if (s2.size()) {
sum += s2.top();
s2.pop();
}
carry_on = sum / 10;
prev = new ListNode(sum % 10);
prev->next = curr;
curr = prev;
}
return curr;
}
};
``````