43. Multiply Strings 字符串相乘

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

Note:

1. The length of both num1 and num2 is < 110.

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

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class Solution1:     def multiply(self, num1, num2):         """         :type num1: str         :type num2: str         :rtype: str         """         if num1 is "0" or num2 is "0":             return "0"         pos = [[] for i in range(len(num1) + len(num2))]         startIndex = 0         for i in range(len(num2) - 1, -1, -1):             curStartIndex = 0             for j in range(len(num1) - 1, -1, -1):                 cur = str(int(num2[i]) * int(num1[j]))                 curIndex = 0                 for k in range(len(cur) - 1, -1, -1):                     pos[startIndex + curStartIndex + curIndex].append(cur[k])                     curIndex += 1                 curStartIndex += 1             startIndex += 1           res = ""         carry = 0         index = 0         while index < len(pos) or carry:             val = carry             for cur in pos[index]:                 val += int(cur)             carry = int(val / 10)             res = str(val % 10) + res             index += 1         return res.lstrip("0")     class Solution2:     def multiply(self, num1, num2):         res = 0         for i in range(len(num1)):             res *= 10             n = int(num1[i])             temp_n = 0             for j in range(len(num2)):                 temp_n *= 10                 temp_n += int(num2[j]) * n             res += temp_n         return str(res)     s = Solution1() num1 = "999" num2 = "999" res = s.multiply(num1, num2) print(res)

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