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multiply-strings.py
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multiply-strings.py
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# Time: O(m * n)
# Space: O(m + n)
class Solution(object):
def multiply(self, num1, num2):
"""
:type num1: str
:type num2: str
:rtype: str
"""
result = [0]*(len(num1)+len(num2))
for i in reversed(xrange(len(num1))):
for j in reversed(xrange(len(num2))):
result[i+j+1] += int(num1[i])*int(num2[j])
result[i+j] += result[i+j+1]//10
result[i+j+1] %= 10
for i in xrange(len(result)):
if result[i]:
break
return "".join(map(lambda x: str(x), result[i:]))
# Time: O(m * n)
# Space: O(m + n)
class Solution2(object):
def multiply(self, num1, num2):
"""
:type num1: str
:type num2: str
:rtype: str
"""
num1, num2 = num1[::-1], num2[::-1]
result = [0]*(len(num1)+len(num2))
for i in xrange(len(num1)):
for j in xrange(len(num2)):
result[i+j] += int(num1[i])*int(num2[j])
result[i+j+1] += result[i+j]//10
result[i+j] %= 10
for i in reversed(xrange(len(result))):
if result[i]:
break
return "".join(map(str, result[i::-1]))
# Time: O(m * n)
# Space: O(m + n)
# Using built-in bignum solution.
class Solution3(object):
def multiply(self, num1, num2):
"""
:type num1: str
:type num2: str
:rtype: str
"""
return str(int(num1) * int(num2))