[415]Add Strings

Given two non-negative numbers 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.

思路

将每一位分别转换为整型然后相加。

Code

Python

class Solution(object):
    def addStrings(self, num1, num2):
        """
        :type num1: str
        :type num2: str
        :rtype: str
        """
        carry = 0
        result = ''
        len1 = len(num1)
        len2 = len(num2)
        while len1 or len2 or carry:
            digit = carry
            if len1:
                len1 -= 1
                digit += ord(num1[len1])-48
            if len2:
                len2 -= 1
                digit += ord(num2[len2])-48
            carry = digit > 9
            result += str(digit % 10)
        return result[::-1]

Runtime: 52ms