14 lines
230 B
Ruby
14 lines
230 B
Ruby
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class Integer
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# binomial coefficient: n C k
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def choose(k)
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# n!/(n-k)!
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pTop = (self-k+1 .. self).inject(1, &:*)
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# k!
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pBottom = (2 .. k).inject(1, &:*)
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pTop / pBottom
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end
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end
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p 5.choose(3)
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p 60.choose(30)
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