Add Strings

Add Strings

Given two non-negative integers num1 and num2 represented as string, return the sum of num1 and num2.

Note

The length of both num1 and num2 is < 5100.
Both num1 and num2 contains only digits 0-9.
Both num1 and num2 does not contain any leading zero.
You must not use any built-in BigInteger library or convert the inputs to integer directly.

Solution

class Solution:
    def addStrings(self, num1, num2):
        """
        :type num1: str
        :type num2: str
        :rtype: str
        """
        list_num = [0]*(max(len(num1), len(num2))+1)
        num1 = num1[::-1]
        num2 = num2[::-1]
        ret = ''
        carry = 0
        for i in range(max(len(num1), len(num2))+1):
            a = int(num1[i]) if i<len(num1) else 0
            b = int(num2[i]) if i<len(num2) else 0           
            digit = (a+b+carry)%10
            carry = (a+b+carry)//10
            list_num[i] = digit
        list_num.reverse()
        for num in list_num:
            ret += str(num)
        if ret[0]=='0':
            ret = ret[1::]
        return ret