diff --git a/extra/project-euler/037/037.factor b/extra/project-euler/037/037.factor new file mode 100644 index 0000000000..f2d5d17c4d --- /dev/null +++ b/extra/project-euler/037/037.factor @@ -0,0 +1,52 @@ +! Copyright (c) 2008 Aaron Schaefer. +! See http://factorcode.org/license.txt for BSD license. +USING: kernel math math.parser math.primes sequences ; +IN: project-euler.037 + +! http://projecteuler.net/index.php?section=problems&id=37 + +! DESCRIPTION +! ----------- + +! The number 3797 has an interesting property. Being prime itself, it is +! possible to continuously remove digits from left to right, and remain prime +! at each stage: 3797, 797, 97, and 7. Similarly we can work from right to +! left: 3797, 379, 37, and 3. + +! Find the sum of the only eleven primes that are both truncatable from left to +! right and right to left. + +! NOTE: 2, 3, 5, and 7 are not considered to be truncatable primes. + + +! SOLUTION +! -------- + + [ + dup prime? [ r-trunc? ] [ drop f ] if + ] [ + drop t + ] if ; + +: reverse-digits ( n -- m ) + number>string reverse 10 string>integer ; + +: l-trunc? ( n -- ? ) + reverse-digits 10 /i reverse-digits dup 0 > [ + dup prime? [ l-trunc? ] [ drop f ] if + ] [ + drop t + ] if ; + +PRIVATE> + +: euler037 ( -- answer ) + 23 1000000 primes-between [ r-trunc? ] subset [ l-trunc? ] subset sum ; + +! [ euler037 ] 100 ave-time +! 768 ms run / 9 ms GC ave time - 100 trials + +MAIN: euler037 diff --git a/extra/project-euler/project-euler.factor b/extra/project-euler/project-euler.factor index feef9dbfa8..fbb62961a9 100644 --- a/extra/project-euler/project-euler.factor +++ b/extra/project-euler/project-euler.factor @@ -11,8 +11,8 @@ USING: definitions io io.files kernel math.parser sequences vocabs project-euler.025 project-euler.026 project-euler.027 project-euler.028 project-euler.029 project-euler.030 project-euler.031 project-euler.032 project-euler.033 project-euler.034 project-euler.035 project-euler.036 - project-euler.067 project-euler.134 project-euler.169 project-euler.173 - project-euler.175 ; + project-euler.037 project-euler.067 project-euler.134 project-euler.169 + project-euler.173 project-euler.175 ; IN: project-euler