Tidying

[project-euler.git] / primes.rb

diff --git a/primes.rb b/primes.rb
index 0febe8007f617dd2b3ecbca2eae02a72ef41cd57..b254fab4f52ac97852e7f5867a5bb311960f3cde 100644 (file)
--- a/primes.rb
+++ b/primes.rb
@@ -28,7 +28,9 @@ class Primes
 
   def next_prime
     candidate = next_candidate(@primes[-1])
-    while @primes.any? {|i| candidate % i == 0 }
+    limit = Math.sqrt(candidate).floor
+    index = @primes.bsearch_index {|i| i > limit} || @primes.length
+    while @primes[0..index].any? {|i| candidate % i == 0 }
       candidate = next_candidate(candidate)
     end
     candidate
@@ -90,11 +92,32 @@ class Primes
   end
   
   def include?(n)
-    while n >= @primes.max
+    while n >= @primes.last
       add_next_prime!
     end
-    @primes.include?(n)
+    !!(@primes.bsearch {|i| n - i})
+  end
+
+  # Use this if you're only testing a few primes and not needing to generate many more.
+  def is_prime?(n)
+    return true if n == 2
+    return false if n < 2
+    limit = Math.sqrt(n).floor
+    while @primes.last <= limit
+      add_next_prime!
+    end
+    index = @primes.bsearch_index {|i| i > limit} || @primes.length
+    @primes[0..index].none? {|i| n % i == 0}
   end
 
 end
 
+
+class Integer
+  @@primes = Primes.instance
+  
+  def prime?
+    @@primes.include? self
+    # @@primes.is_prime? self
+  end
+end