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33 lines
630 B
Python
33 lines
630 B
Python
""" Multiply two numbers using Karatsuba algorithm """
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def karatsuba(a, b):
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"""
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>>> karatsuba(15463, 23489) == 15463 * 23489
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True
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>>> karatsuba(3, 9) == 3 * 9
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True
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"""
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if len(str(a)) == 1 or len(str(b)) == 1:
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return a * b
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m1 = max(len(str(a)), len(str(b)))
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m2 = m1 // 2
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a1, a2 = divmod(a, 10**m2)
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b1, b2 = divmod(b, 10**m2)
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x = karatsuba(a2, b2)
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y = karatsuba((a1 + a2), (b1 + b2))
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z = karatsuba(a1, b1)
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return (z * 10 ** (2 * m2)) + ((y - z - x) * 10 ** (m2)) + (x)
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def main():
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print(karatsuba(15463, 23489))
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if __name__ == "__main__":
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main()
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