[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