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comp.lang.ruby

Re: Weird Numbers (#57) Solution

Zed Lopez

12/8/2005 8:49:00 AM

I was impressed when I started going through 1..1000 in under 15
seconds, so this is much slower than others report. I'm just going to
tell myself you all have much faster computers, and go to bed.

require 'set'

class Subsets
def initialize(set, start)
@set = set.to_a.uniq.sort
@num_elements = start - 1
@map = {}
@set.each_with_index {|k, v| @map[k] = v+1}
end

# returns each subset, in turn. Returns nil when there are no more
def succ
if @combo == nil or @combo == @set[-@num_elements..-1]
return nil if (@num_elements +=1) > @set.length
@combo = @set[0,@num_elements]
else
index = (1..@num_elements).find {|i| @combo[-i] < @set[-i]}
@combo[-index, index] = @set[@map[@combo[-index]], index]
end
@combo
end

def find
while(x = succ)
break if yield x
end
x
end
end

class Integer

def proper_divisors
return [] if self < 2
div = Set.new [1]
2.upto(Math.sqrt(Float.induced_from(self)).to_i) {|i|
quotient, modulus = self.divmod(i)
div.merge([i,quotient]) if modulus.zero?
}
div.to_a.sort
end

def abundant?
self > 11 and [0].concat(proper_divisors).inject {|sum,n| sum += n}
> self
end

def semiperfect?
return nil if self < 6
subsets = Subsets.new(proper_divisors, 2)
subsets.find {|subset| [0].concat(subset).inject {|sum,n| sum += n}
== self }
end

def weird?
self > 69 and abundant? and not semiperfect?
end
end

n = gets.strip
exit if n =~ /\D/ or n !~ /[^0]/
p (1..n.to_i).find_all {|i| i.weird? }

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