## LeetCode 415 Add Strings Problem

``````class Solution(object):
#     """
#     :type num1: str
#     :type num2: str
#     :rtype: str
#     """
#     if num1 is None:
#         num1 = '0'
#     if num2 is None:
#         num2 = '0'
#     res = []
#     carry = 0
#     ls = min(len(num1), len(num2))
#     pos = -1
#     while pos + ls >= 0:
#         curr = int(num1[pos]) + int(num2[pos]) + carry
#         res.insert(0, str(curr % 10))
#         carry = curr / 10
#         pos -= 1
#     while pos + len(num1) >= 0:
#         curr = int(num1[pos]) + carry
#         res.insert(0, str(curr % 10))
#         carry = curr / 10
#         pos -= 1
#     while pos + len(num2) >= 0:
#         curr = int(num2[pos]) + carry
#         res.insert(0, str(curr % 10))
#         carry = curr / 10
#         pos -= 1
#     if carry != 0:
#         res.insert(0, str(carry))
#     return ''.join(res)

res = []
pos1 = len(num1) - 1
pos2 = len(num2) - 1
carry = 0
# This conditon is great
while pos1 >= 0 or pos2 >= 0 or carry == 1:
digit1 = digit2 = 0
if pos1 >= 0:
digit1 = ord(num1[pos1]) - ord('0')
if pos2 >= 0:
digit2 = ord(num2[pos2]) - ord('0')
res.append(str((digit1 + digit2 + carry) % 10))
carry = (digit1 + digit2 + carry) / 10
pos1 -= 1
pos2 -= 1
# reverse res
return ''.join(res[::-1])
``````