Add Two Numbers | Problems

You are given two non-empty linked lists representing two non-negative integers stored in reverse order. Each node contains a single digit. Add the two numbers and return the sum as a linked list.

Example: Input: l1 = [2,4,3], l2 = [5,6,4] → Output: [7,0,8] (342 + 465 = 807)

Sample Input

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Sample Output

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Constraints

Each linked list has 1 to 100 nodes
0 <= Node.val <= 9
Numbers do not have leading zeros

Test Cases

Case 1

Args: [[2,4,3],[5,6,4]] Expected: [7,0,8]

Case 2

Args: [[0],[0]] Expected: [0]

Topics

Linked List

Elementary Math with Carry

Traverse both lists simultaneously, summing digits with carry.

function addTwoNumbers(l1, l2) {
  let dummy = {val: 0, next: null}, curr = dummy, carry = 0;
  while (l1 || l2 || carry) {
    let sum = carry + (l1 ? l1.val : 0) + (l2 ? l2.val : 0);
    carry = Math.floor(sum / 10);
    curr.next = {val: sum % 10, next: null};
    curr = curr.next;
    if (l1) l1 = l1.next;
    if (l2) l2 = l2.next;
  }
  return dummy.next;
}

Time: O(max(m, n)) | Space: O(max(m, n))

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