[leetcode]Multiply Strings @ Python

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] == '' and len(ans) > 1:
del ans[0]
return ''.join(ans)
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