Solution to Project Euler problem 53

extra/project-euler/053/053.factor

@@ -0,0 +1,35 @@
+! Copyright (c) 2008 Aaron Schaefer.
+! See http://factorcode.org/license.txt for BSD license.
+USING: combinators.lib kernel math math.combinatorics math.ranges sequences ;
+IN: project-euler.053
+
+! http://projecteuler.net/index.php?section=problems&id=53
+
+! DESCRIPTION
+! -----------
+
+! There are exactly ten ways of selecting three from five, 12345:
+
+!     123, 124, 125, 134, 135, 145, 234, 235, 245, and 345
+
+! In combinatorics, we use the notation, 5C3 = 10.
+
+! In general,
+!     nCr = n! / r! * (n - r)!
+! where r ≤ n, n! = n * (n − 1) * ... * 3 * 2 * 1, and 0! = 1.
+
+! It is not until n = 23, that a value exceeds one-million: 23C10 = 1144066.
+
+! How many values of nCr, for 1 ≤ n ≤ 100, are greater than one-million?
+
+
+! SOLUTION
+! --------
+
+: euler053 ( -- answer )
+    23 100 [a,b] [ dup [ nCk ] with map [ 1000000 > ] count ] sigma ;
+
+! [ euler053 ] 100 ave-time
+! 64 ms run / 2 ms GC ave time - 100 trials
+
+MAIN: euler053

extra/project-euler/project-euler.factor

@@ -13,9 +13,9 @@ USING: definitions io io.files kernel math math.parser project-euler.ave-time
     project-euler.033 project-euler.034 project-euler.035 project-euler.036
     project-euler.037 project-euler.038 project-euler.039 project-euler.040
     project-euler.041 project-euler.042 project-euler.043 project-euler.044
-    project-euler.048 project-euler.052 project-euler.067 project-euler.075
+    project-euler.048 project-euler.052 project-euler.053 project-euler.067
-    project-euler.079 project-euler.097 project-euler.134 project-euler.169
+    project-euler.075 project-euler.079 project-euler.097 project-euler.134
-    project-euler.173 project-euler.175 ;
+    project-euler.169 project-euler.173 project-euler.175 ;
 IN: project-euler
 
 <PRIVATE