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 it as a linked list.

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

Example:

789 + 478 = 1267

Input: (9 -> 8 -> 7) + (8 -> 7 -> 4)

Output: 7 -> 6 -> 2 -> 1

class Node: def __init__(self, x, nextNode = None): self.val = x self.next = nextNode def printList(l): value = [] while(l): value.append(l.val) l = l.next print(' -> '.join(map(str, value))) def addTwoNumbers(l1, l2): """ :type l1: Node :type l2: Node :rtype: Node """ sum = l1.val + l2.val carry = int(sum / 10) l3 = Node(sum%10) p1 = l1.next p2 = l2.next p3 = l3 while(p1 != None or p2 != None): sum = carry + ( p1.val if p1 else 0) + ( p2.val if p2 else 0) carry = int(sum/10) p3.next = Node(sum % 10) p3 = p3.next p1 = p1.next if p1 else None p2 = p2.next if p2 else None if(carry > 0): p3.next = Node(carry) return l3 #789 l1 = Node(9, Node(8, Node(7))) printList(l1) #478 l2 = Node(8, Node(7, Node(4))) printList(l2) l3 = addTwoNumbers(l1, l2) printList(l3) print() #342 l1 = Node(2, Node(4, Node(3))) printList(l1) #465 l2 = Node(5, Node(6, Node(4))) printList(l2) l3 = addTwoNumbers(l1, l2) printList(l3)

Output:

9 -> 8 -> 7 8 -> 7 -> 4 7 -> 6 -> 2 -> 1 2 -> 4 -> 3 5 -> 6 -> 4 7 -> 0 -> 8

Hope it helps.

This solution will only work with 3 node list, could it be more generic?

This was the shortest, cleanest and easily readable code I have found thus far on this problem. Thanks!