Add Two Numbers

Leetcode #2, "Medium": Add Two Numbers

These two people explain their solutions quite well.

• Youtube: Pheezx Coding - 4.77K subscribers subscribers "Leetcode 2. - Add Two Numbers - Javascript"
• Youtube: Nikhil Lohia - 23.9K subscribers "Add Two Numbers (LeetCode 2) | Full solution with diagrams | EASIEST EVER | Study Algorithms"

General Resources about LinkedLists

• Youtube: freeCodeCamp - 8.9m subscribers "Linked List - Beau teaches JavaScript"

ChatGPT solution

Below is ChatGPT's solution, with its explanation as comments, which I also like.

class ListNode {
  constructor(val, next = null) {
    this.val = val;
    this.next = next;
  }
}

function addTwoNumbers(l1, l2) {
  // Create a dummy head for the result linked list
  let dummyHead = new ListNode(0);
  let current = dummyHead;  // Initialize a pointer to the current node in the result list
  let carry = 0;  // Initialize carry to 0

  // Iterate through the input linked lists
  while (l1 !== null || l2 !== null) {
    // Get the values of the current nodes in l1 and l2 (or 0 if null)
    let x = (l1 !== null) ? l1.val : 0;
    let y = (l2 !== null) ? l2.val : 0;

    // Calculate the sum of the current digits and the carry
    let sum = x + y + carry;

    // Update carry for the next calculation
    carry = Math.floor(sum / 10);

    // Create a new node with the digit part of the sum, and update the result list
    current.next = new ListNode(sum % 10);
    current = current.next;

    // Move to the next nodes in l1 and l2 if they exist
    if (l1 !== null) l1 = l1.next;
    if (l2 !== null) l2 = l2.next;
  }

  // If there is a carry after the last addition, create a new node for it
  if (carry > 0) {
    current.next = new ListNode(carry);
  }

  // Return the result linked list (starting from the second node, as the first one is the dummy head)
  return dummyHead.next;
}