randito · October 26, 2012 21:42 · Oct 26, 2012
diff --git a/Results b/Results
@@ -0,0 +1,7 @@
+$ time ./perfect_number.rb 8028                                                                                                                                
+6
+28
+496
+./perfect_number.rb 8028  0.53s user 0.01s system 99% cpu 0.544 total
+
+This optimized version is *much* better than the original at https://gist.github.com/3961422
diff --git a/perfect_number2.rb b/perfect_number2.rb
@@ -0,0 +1,20 @@
+#!/usr/bin/env ruby -wKU
+
+if __FILE__ == $PROGRAM_NAME
+
+  range = ARGV.first.to_i
+  raise 'Usage: perfect_number.rb [range]' unless range != 0
+
+  def divisors(number)
+    sqrt = Math.sqrt(number) + 1  # divsors come in pair.. so we can optimize
+    lower_factors = (1..sqrt).select { |value| number % value == 0 }
+    upper_factors = lower_factors.map { |value| number / value }  # i.e. 
+    (lower_factors + upper_factors).uniq
+  end
+
+  range.times do |value|
+    sum_of_divisors = divisors(value).inject { |sum,n| sum + n }
+    puts value if sum_of_divisors == 2 * value
+  end
+
+end