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45 lines
874 B
Python
45 lines
874 B
Python
"""
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Modular Exponential.
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Modular exponentiation is a type of exponentiation performed over a modulus.
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For more explanation, please check https://en.wikipedia.org/wiki/Modular_exponentiation
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"""
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"""Calculate Modular Exponential."""
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def modular_exponential(base: int, power: int, mod: int):
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"""
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>>> modular_exponential(5, 0, 10)
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1
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>>> modular_exponential(2, 8, 7)
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4
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>>> modular_exponential(3, -2, 9)
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-1
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"""
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if power < 0:
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return -1
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base %= mod
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result = 1
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while power > 0:
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if power & 1:
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result = (result * base) % mod
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power = power >> 1
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base = (base * base) % mod
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return result
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def main():
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"""Call Modular Exponential Function."""
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print(modular_exponential(3, 200, 13))
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if __name__ == "__main__":
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import doctest
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doctest.testmod()
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main()
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