原题地址：https://oj.leetcode.com/problems/multiply-strings/
题意：
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.
解题思路：两个非负数字字符串的相乘。其实就是大数乘法。算法的关键是要先将两个字符串翻转过来，然后按位进行相乘，相乘后的数不要着急进位，而是存储在一个数组里面，然后将数组中的数对10进行求余（%），就是这一位的数，然后除以10，即/10，就是进位的数。注意最后要将相乘后的字符串前面的0去掉。
代码：
class Solution: # @param num1, a string # @param num2, a string # @return a string def multiply(self, num1, num2): num1 = num1[::-1]; num2 = num2[::-1] arr = [0 for i in range(len(num1)+len(num2))] for i in range(len(num1)): for j in range(len(num2)): arr[i+j] += int(num1[i]) * int(num2[j]) ans = [] for i in range(len(arr)): digit = arr[i] % 10 carry = arr[i] / 10 if i < len(arr)-1: arr[i+1] += carry ans.insert(0, str(digit)) while ans[0] == ‘0‘ and len(ans) > 1: del ans[0] return ‘‘.join(ans)