code golf

7月 202018

"Code golf" is a fun programming pastime that challenges you to solve a problem with the least amount of code possible. Like regular golf, the goal is to use fewest code "strokes" to hit the mark. Here's a recent challenge that was posted to me via Twitter.

While I feel that I can solve nearly any problem (that I can understand) using SAS, my knowledge of the SAS language is quite limited when compared to that of many experts.  And so, I reached out to the SAS Support Communities for help on this one.

The answers were quick, creative, and diverse.  I'll share a few of them here.

The winner, in terms of concision, came from FreelanceReinhard.  He supplied a macro-function one-liner:


With this entry, FreelanceReinhard defied a natural algorithmic instinct to treat this as a numerical digit comparison problem, and instead approached it as simple pattern matching problem.  The highest digit comes from a finite set (0..9).  COMPRESS function is often used to eliminate matching characters from a string, but the k directive inverts the action to keep only the matching characters instead.

If you wanted to use the more traditional approach of looping through values, comparing, and keeping just the maximum value, then you can hardly do better than the code offered by hashman.

do j = 1 to length (str) ; 
  d = d <> input (char (str, j), 1.) ;
end ;

Experienced SAS programmers will remember that

AhmedAl_Attar offered the most dangerous approach, using memory manipulation techniques to populate members of an array:

array ct [20] $1 _temporary_;
call pokelong (str,addrlong(ct[1]),length(str));
c=max(of ct{*});

Visit the communities topic and chime in.

data max;
  str = '00112010302';
  /* novinosrin's approach */
  /* FreelanceReinhard's approach */
  /* AhmedAl_Attar's approach using POKELONG */
  array ct [20] $1 _temporary_;
  call pokelong (str,addrlong(ct[1]),length(str));
  c=max(of ct{*});
  /* loop approach from hashman */
  /* remember that <> is MAX    */
  do j = 1 to length (str) ;            
    d = d <> input (char (str, j), 1.) ;
  end ;
drop j;
/* FreelanceReinhard's approach in a one-liner macro function */
%let str=00112010302;
%put max=%sysfunc(findc(123456789,&str.,b));
/* IML approach from ChanceTGardener */
/* Requires SAS/IML to run           */
proc iml;
  print maximum;

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