2. Add Two Numbers.py

'''
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.
'''

# 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
        """
        summ = 0
        carry = 0
        head = ListNode(0)
        current = head
        while l1 or l2 or carry!=0:
            d1 = l1.val if l1 else 0
            d2 = l2.val if l2 else 0
            s = d1 + d2 + carry
            summ = s%10
            carry = s//10
            current.next = ListNode(summ)
            current = current.next
            if l1 : l1 = l1.next
            if l2 : l2 = l2.next
        return head.next