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Ingy döt Net 2023-07-01 11:58:00 -04:00
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Task/Circular-primes/REXX/circular-primes.rexx Normal file
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/*REXX program finds & displays circular primes (with a title & in a horizontal format).*/
parse arg N hp . /*obtain optional arguments from the CL*/
if N=='' | N=="," then N= 19 /* " " " " " " */
if hp=='' | hp=="," then hip= 1000000 /* " " " " " " */
call genP /*gen primes up to hp (200,000). */
q= 024568 /*digs that most circular P can't have.*/
found= 0; $= /*found: circular P count; $: a list.*/
do j=1 until found==N; p= @.j /* [↓] traipse through all the primes.*/
if p>9 & verify(p, q, 'M')>0 then iterate /*Does J contain forbidden digs? Skip.*/
if \circP(p) then iterate /*Not circular? Then skip this number.*/
found= found + 1 /*bump the count of circular primes. */
$= $ p /*add this prime number ──► $ list. */
end /*j*/ /*at this point, $ has a leading blank.*/
say center(' first ' found " circular primes ", 79, '─')
say strip($)
exit 0 /*stick a fork in it, we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
circP: procedure expose @. !.; parse arg x 1 ox /*obtain a prime number to be examined.*/
do length(x)-1; parse var x f 2 y /*parse X number, rotating the digits*/
x= y || f /*construct a new possible circular P. */
if x<ox then return 0 /*is number < the original? ¬ circular*/
if \!.x then return 0 /* " " not prime? ¬ circular*/
end /*length(x)···*/
return 1 /*passed all tests, X is a circular P.*/
/*──────────────────────────────────────────────────────────────────────────────────────*/
genP: @.1=2; @.2=3; @.3=5; @.4=7; @.5=11; @.6=13; @.7=17; @.8=19 /*assign Ps; #Ps*/
!.= 0; !.2=1; !.3=1; !.5=1; !.7=1; !.11=1; !.13=1; !.17=1; !.19=1 /* " primality*/
#= 8; sq.#= @.# **2 /*number of primes so far; prime square*/
do j=@.#+4 by 2 to hip; parse var j '' -1 _ /*get last decimal digit of J. */
if _==5 then iterate; if j// 3==0 then iterate; if j// 7==0 then iterate
if j//11==0 then iterate; if j//13==0 then iterate; if j//17==0 then iterate
do k=8 while sq.k<=j /*divide by some generated odd primes. */
if j // @.k==0 then iterate j /*Is J divisible by P? Then not prime*/
end /*k*/ /* [↓] a prime (J) has been found. */
#= #+1; !.j= 1; sq.#= j*j; @.#= j /*bump P cnt; assign P to @. and !. */
end /*j*/; return