25 lines
566 B
Ruby
25 lines
566 B
Ruby
def halve(x) = x/2
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def double(x) = x*2
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# iterative
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def ethiopian_multiply(a, b)
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product = 0
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while a >= 1
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p [a, b, a.even? ? "STRIKE" : "KEEP"] if $DEBUG
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product += b unless a.even?
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a = halve(a)
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b = double(b)
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end
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product
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end
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# recursive
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def rec_ethiopian_multiply(a, b)
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return 0 if a < 1
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p [a, b, a.even? ? "STRIKE" : "KEEP"] if $DEBUG
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(a.even? ? 0 : b) + rec_ethiopian_multiply(halve(a), double(b))
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end
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$DEBUG = true # $DEBUG also set to true if "-d" option given
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a, b = 20, 5
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puts "#{a} * #{b} = #{ethiopian_multiply(a,b)}"; puts
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