Addition of two linked-lists as non-negative integers.

solution.js

/*
You are given two 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.

Example:

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.
*/

class Node {
    constructor(val, next) {
        this.value = val;
        this.next = next;
    }
}

const numberOne = new Node(
    2,
    new Node(
        4,
        new Node(
            3
        )
    )
);

const numberTwo = new Node(
    5,
    new Node(
        6,
        new Node(
            4
        )
    )
);

const addReverseLists = (one, two) => {
    let carry = 0;
    let leftCurrent = one;
    let rightCurrent = two;
    let tempSum;
    let resultList;
    let resultCurrent;

    while (leftCurrent || rightCurrent) {
        if (!rightCurrent) { // Only the left digit is present
            tempSum = leftCurrent.value + carry;
            leftCurrent = leftCurrent.next;
        } else if (!leftCurrent) { // Only the right digit is present
            tempSum = rightCurrent.value + carry;
            rightCurrent = rightCurrent.next;
        } else { // Both the digits are present
            tempSum = leftCurrent.value + rightCurrent.value + carry;
            leftCurrent = leftCurrent.next;
            rightCurrent = rightCurrent.next;
        }

        if (tempSum > 9) { // In case of a carry
            carry = Math.floor(tempSum / 10);
            tempSum = tempSum - (carry * 10);
        }

        if (!resultList) { // Only for the first time
            resultCurrent = new Node(tempSum);
            resultList = resultCurrent;
        } else { // For successive times
            resultCurrent.next = new Node(tempSum);
            resultCurrent = resultCurrent.next;
        }
    }

    // Add another most-significant digit in case of a carry
    if (carry) {
        resultCurrent.next = new Node(carry);
    }

    return resultList;
};

console.log(addReverseLists(numberOne, numberTwo));