[LeetCode]题解（python）：043-Multiply Strings

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题目来源

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https://leetcode.com/problems/multiply-strings/

Given two numbers represented as strings, return multiplication of the numbers as a string.

Note: The numbers can be arbitrarily large and are non-negative.

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题意分析

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Input: two numbers expressed as string

Output:the multiply of the two sums

Conditions:数可以无限大，做两个数的乘法

如："23650379502752" 和 "865382861454"

结果："20466633088564555427721408"

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题目思路

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首先将两个str转化为整数的list，然后考虑到乘积的位数必然小于等于len（str1）+len（str2），先初始化乘积为0的list，然后按照位数相乘的规律去做

注意：

1 最后结果需要将大数的0去掉，同时如果结果为0需要返回串“0”

2 翻转：mul.reverse()

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AC代码（Python）

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 _author_ = "YE"
 # -*- coding:utf-8 -*-

 class Solution(object):
     def multiply(self, num1, num2):
         """
         :type num1: str
         :type num2: str
         :rtype: str
         """
         len1 = len(num1)
         len2 = len(num2)

         list1 = [0 for i in range(len1)]
         list2 = [0 for i in range(len2)]

         for i in range(len1):
             list1[len1 - 1 - i] = int(num1[i])
         for i in range(len2):
             list2[len2 - 1 -i] = int(num2[i])

         # print(list1,list2)

         mul = [0 for i in range(len1 + len2)]

         for i in range(len2):
             carry = 0
             for j in range(len1):
                 mul[i + j] = mul[i + j] + carry + (list2[i] * list1[j]) % 10

                 carry = (list2[i] * list1[j]) // 10

                 if mul[i + j] >= 10:
                     carry = carry + mul[i + j] // 10
                     mul[i + j] = mul[i + j] % 10

             if carry > 0:
                 mul[i + len1] += carry
                 if mul[i + len1] > 10:
                     mul[i + len1] = mul[i + len1] % 10
                     carry += mul[i + len1] // 10

         index = len1 + len2 - 1
         while index >= 0:
             if mul[index] > 0:
                 break
             index -= 1

         if index + 1 < len1 + len2:
             mul[index+1:] = []

         mul.reverse()

         s = ''
         for i in range(len(mul)):
             s += str(mul[i])
         if s == '':
             s = ''
         return s

 str1 = ''
 str2 = ''
 s = Solution()

 print(s.multiply(str1,str2))