[leetcode] Add Two Numbers

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

思路：思路很简单，类似add binary， 逐位比较，过十进位

# Definition for singly-linked list.# class ListNode:#     def __init__(self, x):#         self.val = x#         self.next = Noneclass Solution:    # @return a ListNode    def addTwoNumbers(self, l1, l2):        newhead = ListNode(0)        head1 = l1        head2 = l2        node = newhead        carry = 0        while head1 != None or head2 != None:            val1 = head1.val if head1 != None else 0            val2 = head2.val if head2 != None else 0            val = val1 + val2 + carry            node.next = ListNode(val % 10)            carry = val / 10            node = node.next            head1 = head1.next if head1 != None else head1            head2 = head2.next if head2 != None else head2        if carry == 0:            node.next = None        else:            node.next = ListNode(1)            node.next.next =None        return newhead.next