Leetcode||43. Multiply Strings

Given two non-negative integers 

num1

 and 

num2

 represented
as strings, return the product of 

num1

 and 

num2

.

Note:
The length of both 

num1

 and 

num2

 is
< 110.
Both 

num1

 and 

num2

 contains
only digits 

0-9

.
Both 

num1

 and 

num2

 does
not contain any leading zero.
You must not use any built-in BigInteger library or convert the inputs to integer directly.

大数相乘，根据小学的做法，逐个相乘，先累加到相应位置上，然后对逐位乘的结果按位从低位到高位取模，进位
class Solution(object):
def multiply(self, num1, num2):
"""
:type num1: str
:type num2: str
:rtype: str
"""
size1 = len(num1);size2 = len(num2)
if size1 <= 5 and size2 <= 5:
tmp = int(num1) * int(num2)
return str(tmp)
num1 = num1[::-1];num2 = num2[::-1]
array = [0 for i in range(len(num1) + len(num2))]
for i in range(len(num1)):
for j in range(len(num2)):
array[i + j] += int(num1[i]) * int(num2[j])
ans = []
for i in range(len(array)):
digit = array[i] % 10
carry = array[i] / 10
if i < len(array) - 1:
array[i + 1] += carry
ans.insert(0,str(digit))
while ans[0] == '0' and len(ans) > 1:
del ans[0]
return ''.join(ans)