0002-add-two-numbers.ts

/**
 * Definition for singly-linked list.
 * class ListNode {
 *     val: number
 *     next: ListNode | null
 *     constructor(val?: number, next?: ListNode | null) {
 *         this.val = (val===undefined ? 0 : val)
 *         this.next = (next===undefined ? null : next)
 *     }
 * }
 */

function addTwoNumbers(
    l1: ListNode | null,
    l2: ListNode | null
): ListNode | null {
    let dummyNode: ListNode = new ListNode();
    let currentNode: ListNode = dummyNode;
    let carry: number = 0;

    while (l1 !== null || l2 !== null || carry !== 0) {
        const val1 = l1 !== null ? l1.val : 0;
        const val2 = l2 !== null ? l2.val : 0;

        const sum: number = val1 + val2 + carry;
        const value: number = sum % 10;
        const newLinkedList: ListNode = new ListNode(value);
        currentNode.next = newLinkedList;
        currentNode = newLinkedList;
        carry = Math.floor(sum / 10);

        l1 = l1 !== null ? l1.next : null;
        l2 = l2 !== null ? l2.next : null;
    }

    return dummyNode.next;
}