Add Two Numbers LeetCode

addTwoNumbers.js

/*
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.
 
Example 1:
Input: l1 = [2,4,3], l2 = [5,6,4]
Output: [7,0,8]
Explanation: 342 + 465 = 807.
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.
*/

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} l1
 * @param {ListNode} l2
 * @return {ListNode}
 */
 var addTwoNumbers = function(l1, l2) {
    let head, c= head,  one = l1, two = l2, carry = 0;
  
    while(one || two) {
        let x = 0, y = 0, sum = carry, next, tmpNode;
        if (one.val) {
            x = one.val;
        }
        
        if (two.val) {
            y = two.val;
        }
        
        sum += x + y;
        carry = Math.floor(sum / 10);
        next = sum % 10;
        tmpNode = new ListNode(next);
        
        if (head == null) {
            head =  new ListNode(next);
            c = head;
        } else{
            c.next = tmpNode;
            c = c.next;
        }
        
        if (one.next != null) {
            one = one.next;
        } else{
            one = false
        }
        
        if (two.next != null) {
            two = two.next;
        } else{
            two = false
        }
    }
    
    if (carry > 0) {
        let tmpNode= new ListNode(carry);
        c.next = tmpNode;
    }
    return head;
};

console.log(addTwoNumbers([3,4,5], [7,9,1]))