add_two_numbers.py

# problem description: https://leetcode.com/problems/add-two-numbers/

# 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
        """
        carry = 0
        head = ListNode(0)
        curr = head
        while l1 or l2:
            v1 = l1.val if l1 else 0
            v2 = l2.val if l2 else 0
            val = (v1+v2+carry) % 10
            carry = (v1+v2+carry) / 10
            curr.next = ListNode(val)
            curr = curr.next
            if l1: l1 = l1.next
            if l2: l2 = l2.next
        
        if carry == 1:
            curr.next = ListNode(1)
            
        return head.next