leetcode 2. Add Two Numbers

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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.

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# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None
class ListNode2(ListNode):
    def __init__(self, x):
        self.val = x
        self.next = None
    
    def append(self, dataOrNode):
        item = None
        if isinstance(dataOrNode, ListNode):
            item = dataOrNode
        else:
            item = ListNode(dataOrNode)

        if not self:
            self = item
        else:
            node = self
            while node.next:
                node = node.next
            node.next = item

class Solution:
    def addTwoNumbers(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        list1 = []
        list2 = []
        while l1:
            list1.append(l1.val)
            l1 = l1.next
            
        while l2:
            list2.append(l2.val)
            l2 = l2.next
        int1 = 0
        for i in range(len(list1)):
            int1 += (10**i)*list1[i]
        
        int2 = 0
        for i in range(len(list2)):
            int2 += (10**i)*list2[i]
        
        int_target = int1 + int2
        p = ListNode2(int_target % 10)
        int_target = int_target // 10
        while int_target:
            p.append(int_target % 10)
            int_target = int_target // 10
        return p