[**Problem Link**]

Hello,

Here’s my solution for the add two numbers problem on LeetCode.

**Example:**

**Input:** (2 -> 4 -> 3) + (5 -> 6 -> 4)
**Output:** 7 -> 0 -> 8
**Explanation:** 342 + 465 = 807.

When doing problems on websites such as LeetCode, I like to code in my own IDE, that’s why you’ll see some additional helper functions besides the solution code.

class Solution(object):
def _get_append_func(self, root):
_root = root
def __add_to_list(value):
nonlocal _root
_root.next = ListNode(value)
_root = _root.next
return __add_to_list
def _compute(self, result, base=10):
carry = result // base
rest = result % base
return carry, rest
def addTwoNumbers(self, l1, l2):
"""
:type l1: ListNode
:type l2: ListNode
:rtype: ListNode
"""
root_node = None
root_append_func = None
term_1 = l1
term_2 = l2
saved_carry = 0
while True:
# end of expression ; add cary if any
if term_1 is None and term_2 is None:
if saved_carry > 0:
root_append_func(saved_carry)
break
# We haven't reached the end, we assume that whatever term is left is 0
if term_1 is None:
term_1 = ListNode(0)
if term_2 is None:
term_2 = ListNode(0)
# add the two terms
term_sum_carry, term_sum_no_carry = self._compute(term_1.val + term_2.val)
# add sum to current carry
next_carry, total_with_carry = self._compute(term_sum_no_carry + saved_carry)
# save carry
saved_carry = term_sum_carry + next_carry
# save total
if not root_node:
root_node = ListNode(total_with_carry)
root_append_func = self._get_append_func(root_node)
else:
root_append_func(total_with_carry)
# move on
term_1 = term_1.next
term_2 = term_2.next
return root_node

My solution isn’t that great because of the **_add_to_list** function which iterates the root_node to append the next value. I have no idea how to optimize that right now.

UPDATE:

I’ve learnt about **nonlocal** and found a way to slightly optimize my code:

def _get_append_func(self, root):
_root = root
def __add_to_list(value):
nonlocal _root
_root.next = ListNode(value)
_root = _root.next
return __add_to_list

Thanks for reading!

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