Reply to thread

Message: [QUOTE="Dave Burt, post: 4495172"] I have a solution for the "effectively useless" basket. It's a naive algorithm, and I haven't yet received a number above 70 from it. The advantages are that it's straightforward idiomatic Ruby, and core of the algorithm is expressed about as tersely as Martin's definition. And I like my ArraySubsetList class. class Fixnum def divisors (1..self).select {|i| self % i == 0 } end end module Enumerable def sum inject(0) {|m, o| m + o } end end class Array def subsets ArraySubsetList.new(self) end end class ArraySubsetList def initialize(array) @array = array end def [](index) return nil unless (0...size) === index ret = [] @array.size.times {|i| ret << @array[i] if index[i] == 1 } ret end def each size.times {|bits| yield self[bits] } end include Enumerable def size 1 << @array.size end alias length size end def wierd_numbers_up_to(max) ret = [] for n in 1..max # A weird number is defined as a number, n, such that the sum of all its divisors # (excluding n itself) is greater than n, but no subset of its divisors sums up to # exactly n. divs = n.divisors divs.delete i if divs.sum > i && divs.subsets.select {|subset| subset.sum == i }.empty? ret << i yield i if block_given? end end ret end if $0 == __FILE__ if ARGV.size == 1 && (ARGV[0].to_i rescue 0) > 0 wierd_numbers_up_to(ARGV[0].to_i) {|n| puts n } else puts "usage: #$0 n\n Find all weird numbers less than n" end end Cheers, Dave[/i][/i] [/QUOTE]