2. Add Two Numbers

2. Add Two Numbers (Medium)

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.

Related Topics:
Linked List, Math

Similar Questions:

• Multiply Strings (Medium)
• Add Binary (Easy)
• Sum of Two Integers (Easy)
• Add Strings (Easy)
• Add Two Numbers II (Medium)
• Add to Array-Form of Integer (Easy)

Solution 1.

// OJ: https://leetcode.com/problems/add-two-numbers/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(1)
class Solution {
public:
    ListNode* addTwoNumbers(ListNode* a, ListNode* b) {
        int carry = 0;
        ListNode dummy, *tail = &dummy;
        while (a || b || carry) {
            if (a) {
                carry += a->val;
                a = a->next;
            }
            if (b) {
                carry += b->val;
                b = b->next;
            }
            tail->next = new ListNode(carry % 10);
            tail = tail->next;
            carry /= 10;
        }
        return dummy.next;
    }
};