Solution to Project Euler problem 37
parent
f86f36794f
commit
6394eb70bf
|
@ -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
|
||||
! --------
|
||||
|
||||
<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
|
|
@ -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
|
||||
|
|
Loading…
Reference in New Issue