Harmonize spelling

[factor.git] / extra / project-euler / 100 / 100.factor

diff --git a/extra/project-euler/100/100.factor b/extra/project-euler/100/100.factor
index d2d396a0e18846b5e4c2b00440192e5bbe8aa358..0ea04961819bb8984777de0b6f3467f39a43498d 100644 (file)
--- a/extra/project-euler/100/100.factor
+++ b/extra/project-euler/100/100.factor
@@ -1,7 +1,35 @@
-USING: kernel sequences math.functions math ;
+! Copyright (c) 2008 Eric Mertens.
+! See http://factorcode.org/license.txt for BSD license.
+USING: kernel math math.functions project-euler.common ;
 IN: project-euler.100
 
-: euler100 ( -- n )
+! http://projecteuler.net/index.php?section=problems&id=100
+
+! DESCRIPTION ! -----------
+
+! If a box contains twenty-one colored discs, composed of fifteen blue discs
+!  and six red discs, and two discs were taken at random, it can be seen that
+!  the probability of taking two blue discs, P(BB) = (15/21)*(14/20) = 1/2.
+
+! The next such arrangement, for which there is exactly 50% chance of taking
+!  two blue discs at random, is a box containing eighty-five blue discs and
+!  thirty-five red discs.
+
+! By finding the first arrangement to contain over 10^12 = 1,000,000,000,000
+!  discs in total, determine the number of blue discs that the box would contain.
+
+
+! SOLUTION
+! --------
+
+: euler100 ( -- answer )
     1 1
-    [ dup dup 1- * 2 * 10 24 ^ <= ]
-    [ tuck 6 * swap - 2 - ] [ ] while nip ;
+    [ dup dup 1 - * 2 * 10 24 ^ <= ]
+    [ [ 6 * swap - 2 - ] keep swap ] while nip ;
+
+! TODO: solution needs generalization
+
+! [ euler100 ] 100 ave-time
+! 0 ms ave run time - 0.14 SD (100 trials)
+
+SOLUTION: euler100