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#!/usr/bin/env python

'''

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

'''

from __future__ import division

import random

class DigitNode(object):

def __init__(self, digit, next=None):

self.digit = digit

self.next = next

def __str__(self):

if next:

return 'DigitNode(%d, %s)' % (self.digit, str(self.next))

else:

return 'DigitNode(%d)' % (self.digit)

def add_two_numbers(a, b):

prev_carry = 0

orig_node = None

prev_node = None

while a and b:

digit = (a.digit + b.digit + prev_carry) % 10

cur_carry = (a.digit + b.digit + prev_carry) // 10

node = DigitNode(digit)

if prev_node: prev_node.next = node

else: orig_node = node

a = a.next

b = b.next

prev_carry = cur_carry

prev_node = node

# leftover

x = a if a else b

while x:

digit = (x.digit + prev_carry) % 10

cur_carry = (x.digit + prev_carry) // 10

node = DigitNode(digit)

if prev_node: prev_node.next = node

x = x.next

prev_carry = cur_carry

prev_node = node

return orig_node

if __name__ == '__main__':

a = DigitNode(2, DigitNode(4, DigitNode(3, DigitNode(5))))

b = DigitNode(5, DigitNode(6, DigitNode(4, DigitNode(1, DigitNode(2)))))

print add_two_numbers(a,b)