Add_Two_Numbers.py

"""
You are given two linked lists representing two non-negative numbers. 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.

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

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

class Solution:
    # @return a ListNode
    def addTwoNumbers(self, l1, l2):
        dummy = ListNode(0)
        carry = 0
        cur = dummy
        while l1 is not None or l2 is not None or carry > 0:
            sum = carry
            if l1 is not None:
                sum += l1.val
                l1 = l1.next
            if l2 is not None:
                sum += l2.val
                l2 = l2.next
            cur.next = ListNode(sum % 10)
            carry = sum / 10
            cur = cur.next
        return dummy.next