Solution to Project Euler problem 37

db4
Aaron Schaefer 2008-01-30 00:50:18 -05:00
parent f86f36794f
commit 6394eb70bf
2 changed files with 54 additions and 2 deletions

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! 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
! --------
<PRIVATE
: r-trunc? ( n -- ? )
10 /i dup 0 > [
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

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@ -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
<PRIVATE