[LeetCode 415] Add Strings(Python)

题目描述

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

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

思路

按加法法则计算。用一个整数变量保存当前进位值，用以相加。

代码

class Solution(object):    def addStrings(self, num1, num2):        """        :type num1: str        :type num2: str        :rtype: str        """        res=''        i = len(num1) -1        j = len(num2) - 1        # 进位值        carry = 0        while i >= 0 and j >= 0:            sum = int(num1[i]) + int(num2[j]) + carry            if sum < 10:                carry = 0                res = str(sum) + res            else:                carry = 1                res = str(sum%10) + res            i -= 1            j -= 1        while i != -1:            sum = int(num1[i]) + carry            if sum < 10:                carry = 0                res = str(sum) + res            else:                carry = 1                res = str(sum % 10) + res            i -= 1        while j != -1:            sum = int(num2[j]) + carry            if sum < 10:                carry = 0                res = str(sum) + res            else:                carry = 1                res = str(sum % 10) + res            j -= 1        if carry != 0:            res = str(carry) + res        return res