Puzzle - RPL and others

[rprosperi]

(04-22-2021 11:52 PM)Valentin Albillo Wrote:  Ok,this 6-liner, 195-byte recursive HP-71B program will do:

      1   DESTROY ALL @ STD @ FOR I=1 TO 9 @ CALL TST((I),2,9) @ NEXT I

      2   SUB TST(N,D,M) @ N=10*N @ FOR I=1 TO 9 @ X=N+I @ IF MOD(X,D) THEN 6
      3   A$=STR$(X) @ FOR J=1 TO LEN(A$) @ IF POS(A$[J+1],A$[J,J]) THEN 6
      4   NEXT J @ IF LEN(A$)=9 THEN DISP X @ END ALL
      5   IF D#M THEN CALL TST(X,D+1,M)
      6   NEXT I

Nice program Valentin!!

This short, elegant program well illustrates the power and flexibility of the 71B's BASIC, clearly showing how its flexible string functions, recursion, call-by-value, etc. can be used to create unexpectedly powerful (if still somewhat slow by today's standards) and compact programs.

I rarely read these contests closely, and even more rarely comment on solutions, but this one really made me smile. Thanks for that!