Add Two Numbers II.py

'''
You are given two non-empty linked lists representing two non-negative integers. The most significant digit comes first 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.

Follow up:
What if you cannot modify the input lists? In other words, reversing the lists is not allowed.

Example:

Input: (7 -> 2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 8 -> 0 -> 7

'''


# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def addTwoNumbers(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        a = 0
        while l1:
            a = a * 10 + l1.val
            l1 = l1.next
        
        b = 0
        while l2:
            b = b* 10 + l2.val
            l2 = l2.next
        
        digits = str(a + b)
        
        dummy = ListNode(0)
        cur = dummy
        for x in digits:
            node = ListNode(int(x))
            cur.next = node
            cur = cur.next
            
        return dummy.next