0002: Add Two Numbers

Problem Statement

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 contains a single digit. Add the two numbers and return the sum as a linked list.

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

Example 1:

Input: l1 = [2,4,3], l2 = [5,6,4]
Output: [7,0,8]
Explanation: 342 + 465 = 807.

Example 2:

Input: l1 = [0], l2 = [0]
Output: [0]

Example 3:

Input: l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9]
Output: [8,9,9,9,0,0,0,1]

Constraints:

  • The number of nodes in each linked list is in the range [1, 100].
  • 0 <= Node.val <= 9
  • It is guaranteed that the list represents a number that does not have leading zeros.

Code Solution

class Solution:
    def addTwoNumbers(self, l1, l2):
    
        result = temp = ListNode(-1, None)
        
        carry = 0
        while l1 or l2:
        
            n1 = 0 if not l1 else l1.val
            n2 = 0 if not l2 else l2.val
            
            total = n1 + n2 + carry
            carry = total // 10
            total = total % 10
            
            temp.next = ListNode(total)
            temp = temp.next
            
            l1 = None if not l1 else l1.next
            l2 = None if not l2 else l2.next
        
        if carry:
            temp.next = ListNode(carry)
            temp = temp.next
        
        return result.next