22 lines
384 B
Ruby
22 lines
384 B
Ruby
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class Integer
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def mod_exp(exp, mod)
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exp < 0 and raise ArgumentError, "negative exponent"
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prod = 1
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base = self % mod
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until exp.zero?
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exp.odd? and prod = (prod * base) % mod
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exp >>= 1
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base = (base * base) % mod
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end
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prod
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end
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end
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PHI = (1 + Math.sqrt(5)) / 2
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def fib(n)
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((PHI ** n - (-1 / PHI) ** n) / Math.sqrt(5)).to_i
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end
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puts fib(8)
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