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

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} l1
 * @param {ListNode} l2
 * @return {ListNode}
 */
var addTwoNumbers = function (l1, l2) {
    var carry = 0;
    var sum = 0;
    var head = new ListNode(0);
    var now = head;
    var a = l1;
    var b = l2;
    while (a !== null || b !== null) {
        sum = (a ? a.val : 0) + (b ? b.val : 0) + carry;
        carry = Math.floor(sum / 10);
        now.next = new ListNode(sum % 10);
        now = now.next;
        a = a ? a.next : null;
        b = b ? b.next : null;
    }
    if (carry) now.next = new ListNode(carry);
    return head.next;
};

Complexity:

• Time complexity: O(max(m,n)).
• Space complexity: O(max(m,n)).