problem 49

Author: lilaboc

49.rb

@@ -0,0 +1,39 @@
+require 'set'
+
+def sieve(below)
+  total = below - 2#00000
+  array = [].fill(0 .. total){false}
+  p = 2
+  loop do
+    unless array[p - 2]
+      2.upto(below / p) do |x|
+        array[x * p - 2] = true
+      end
+    end
+    p += 1
+    break if p > total
+  end
+  result = []
+  array.each_index{|index|result << index + 2 unless array[index]}
+  Set.new(result)
+end
+
+primes = sieve(9999)
+result = Set.new
+primes.select{|x| x >= 1000}.each do |x|
+  mutations = x.to_s.each_char.to_a.permutation.to_a.map(&:join).to_set.to_a.map(&:to_i).select{|x|x>1000}.select{|x|primes.include?(x)}.sort
+  if mutations.size > 2
+    mutations.each_index do |y|
+      if y > 1
+        0.upto(y - 1) do |z|
+          if mutations.include?(mutations[y] * 2 - mutations[z])
+            result.add("#{mutations[z]}#{mutations[y]}#{mutations[y] * 2 - mutations[z]}")
+          end
+        end
+      end
+
+    end
+  end
+end
+result.each{|x|puts x}
+