2 Add Two Numbers ✅¶

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 contain a single digit. Add the two numbers and return it as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Example:

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

Solution: Simulation¶

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

C# Solution¶

namespace Algorithms.Medium
{
  public class ListNode
  {
    public int val;
    public ListNode next;
    public ListNode(int x) { val = x; }
  }
  public static class AddTwoNumbers
  {
    public static ListNode Add(ListNode l1, ListNode l2)
    {
      ListNode tail = new ListNode(0);
      ListNode temp = tail;
      int sum = 0;

      while (l1 != null || l2 != null || sum > 0)
      {
        sum += (l1 == null ? 0 : l1.val) + (l2 == null ? 0 : l2.val);
        tail.next = new ListNode(sum % 10);
        tail = tail.next;

        if (l1 != null) l1 = l1.next;
        if (l2 != null) l2 = l2.next;
        sum /= 10;
      }

      return temp.next;
    }
  }
}

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