Delete empty unit tests files, remove 1- and 1+, reorder IN: lines in a lot of places...

[factor.git] / extra / project-euler / 150 / 150.factor

diff --git a/extra/project-euler/150/150.factor b/extra/project-euler/150/150.factor
index 8c93d4f7e638d3e79670f9c2335aff6e975a2a76..a54b7d1db0faa147fd98c6b2a82ba21efaa163b8 100644 (file)
--- a/extra/project-euler/150/150.factor
+++ b/extra/project-euler/150/150.factor
@@ -1,9 +1,34 @@
-! Copyright (c) 2008 Eric Mertens
+! Copyright (c) 2008 Eric Mertens.
 ! See http://factorcode.org/license.txt for BSD license.
-USING: kernel math math.order sequences sequences.private
-locals hints ;
+USING: hints kernel locals math math.order math.ranges project-euler.common
+    sequences sequences.private ;
 IN: project-euler.150
 
+! http://projecteuler.net/index.php?section=problems&id=150
+
+! DESCRIPTION
+! -----------
+
+! In a triangular array of positive and negative integers, we wish to find a
+! sub-triangle such that the sum of the numbers it contains is the smallest
+! possible.
+
+! In the example below, it can be easily verified that the marked triangle
+! satisfies this condition having a sum of -42.
+
+! We wish to make such a triangular array with one thousand rows, so we
+! generate 500500 pseudo-random numbers sk in the range +/-2^19, using a type of
+! random number generator (known as a Linear Congruential Generator) as
+! follows:
+
+! ...
+
+! Find the smallest possible sub-triangle sum.
+
+
+! SOLUTION
+! --------
+
 <PRIVATE
 
 ! sequence helper functions
@@ -17,30 +42,24 @@ IN: project-euler.150
 : partial-sum-infimum ( seq -- seq )
     0 0 rot [ (partial-sum-infimum) ] each drop ; inline
 
-: generate ( n quot -- seq )
-    [ drop ] prepose map ; inline
-
 : map-infimum ( seq quot -- min )
     [ min ] compose 0 swap reduce ; inline
 
-
 ! triangle generator functions
 
 : next ( t -- new-t s )
     615949 * 797807 + 20 2^ rem dup 19 2^ - ; inline
 
 : sums-triangle ( -- seq )
-    0 1000 [ 1+ [ next ] generate partial-sums ] map nip ; 
-
-PRIVATE>
+    0 1000 [1,b] [ [ next ] replicate partial-sums ] map nip ;
 
 :: (euler150) ( m -- n )
     [let | table [ sums-triangle ] |
         m [| x |
-            x 1+ [| y |
-                m x - [| z |
+            x 1 + [| y |
+                m x - [0,b) [| z |
                     x z + table nth-unsafe
-                    [ y z + 1+ swap nth-unsafe ]
+                    [ y z + 1 + swap nth-unsafe ]
                     [ y        swap nth-unsafe ] bi -
                 ] map partial-sum-infimum
             ] map-infimum
@@ -49,5 +68,12 @@ PRIVATE>
 
 HINTS: (euler150) fixnum ;
 
-: euler150 ( -- n )
+PRIVATE>
+
+: euler150 ( -- answer )
     1000 (euler150) ;
+
+! [ euler150 ] 10 ave-time
+! 30208 ms ave run time - 593.45 SD (10 trials)
+
+SOLUTION: euler150