Re: Compute Unique Numbers in a Set

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From	John Forkosh <forkosh@panix.com>
Newsgroups	comp.lang.c
Subject	Re: Compute Unique Numbers in a Set
Date	Sun, 15 Jan 2023 02:49:50 -0000 (UTC)
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Albert <invalid@gmail.com> wrote:
> Is this the best way to generate unique random numbers in a set of 6 
> numbers? <snip>

I think what you're looking for (not sure whether or not it's already
been mentioned in this long thread) is a "partial permutation",
swapping used numbers with unused ones, but we don't need to save the
used ones. Here's my general solution, and cc -DTESTDRIVE for the
main() test driver...

/* ---
 * uniqrand.c
 * Generate nuniq random numbers in the range lorand...hirand
 * ---
 * (optional) command-line arguments:
 *    ./uniqrand  nuniq  lorand  hirand    seedval
 *                  100       1     999  864297531  <-- default test values
 * ------------------------------------------------------------------------ */

/* --- standard headers --- */
#include <stdio.h>
#include <stdlib.h>
#include <sys/param.h> /* for MIN(i,j) macro */

/* --- standard headers --- */
#include <stdio.h>
#include <stdlib.h>
#include <sys/param.h> /* for MIN(i,j) macro */

/* --- entry point --- */
int *uniqrand ( int nuniq, int lorand, int hirand ) {
  /* --- allocations and declarations --- */
  int  iuniq = 0;                       /* index 0...nuniq-1 */
  int  range = 1+abs(hirand-lorand);    /* random number range */
  int  *randvals  = NULL,               /* nuniq ints returned to caller */
       *rangevals = NULL;               /* all numbers lorand...hirand */
  /* --- initialization --- */
  if ( nuniq<1 || nuniq>range ) goto end_of_job; /* input error */  
  randvals  = (int *)malloc((nuniq+99)*sizeof(int)); /* caller free()'s */
  rangevals = (int *)malloc((range+99)*sizeof(int)); /* we free() work area */
  if ( randvals==NULL || rangevals==NULL ) goto end_of_job; /* malloc error */
  rangevals[0] = MIN(lorand,hirand);    /* in case hirand<lorand */
  for ( iuniq=1; iuniq<range; iuniq++ ) /* all numbers lorand...hirand... */
    rangevals[iuniq] = rangevals[0] + iuniq; /* ...or vice versa */
  /* --- generate nuniq unique random numbers from lorand to hirand --- */
  for ( iuniq=0; iuniq<nuniq; iuniq++ ) {
    int  thisrand = rand()%range;       /* random number 0...range-1 */
    randvals[iuniq] = rangevals[thisrand]; /* unique random lorand...hirand */
    rangevals[thisrand] = rangevals[--range]; } /* replace used number */
  /* --- end-of-job --- */
  end_of_job:
    if ( rangevals != NULL ) free((void *)rangevals);
    return ( randvals );
  } /* --- end-of-function uniqrand() --- */

#if defined(TESTDRIVE)
/* --- entry point --- */
int main ( int argc, char *argv[] ) {
  /* --- command-line arguments --- */
  int    nuniq = ( argc>1? atoi(argv[1]) :       100 ),
        lorand = ( argc>2? atoi(argv[2]) :         1 ),
        hirand = ( argc>3? atoi(argv[3]) :       999 ),
       seedval = ( argc>4? atoi(argv[4]) : 164897532 );
  /* --- allocations and declarations --- */
  int *uniqrand(), *randvals=NULL;      /* randvals from uniqrand() */
  int iuniq = 0;                        /* randvals[] index */
  /* --- initialization --- */
  if ( seedval > 0 ) srand(seedval);    /* initialize rand() */
  /* --- call uniqrand() and display results --- */
  if ( (randvals=uniqrand(nuniq,lorand,hirand)) == NULL ) goto end_of_job;
  for ( iuniq=0; iuniq<nuniq; iuniq++ )
    printf("%7d%s",randvals[iuniq],
           (iuniq==nuniq-1?"\n":((iuniq+1)%8==0?",\n":",")) );
  /* --- end-of-job --- */
  end_of_job:
    if ( randvals != NULL ) free((void *)randvals);
    exit ( 0 );
  } /* --- end-of-function main() --- */
#endif
/* --- end-of-file uniqrand.c --- */

John Forkosh  ( mailto:  j@f.com  where j=john and f=forkosh )

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Compute Unique Numbers in a Set Albert <invalid@gmail.com> - 2022-12-26 23:45 +0000
  Re: Compute Unique Numbers in a Set "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2022-12-26 16:52 -0800
    Re: Compute Unique Numbers in a Set tTh <tth@none.invalid> - 2022-12-27 02:44 +0100
      Re: Compute Unique Numbers in a Set "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2022-12-27 13:35 -0800
  Re: Compute Unique Numbers in a Set Richard Damon <Richard@Damon-Family.org> - 2022-12-26 20:47 -0500
    Re: Compute Unique Numbers in a Set Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-12-27 15:57 +0000
      Re: Compute Unique Numbers in a Set Richard Damon <Richard@Damon-Family.org> - 2022-12-27 11:16 -0500
        Re: Compute Unique Numbers in a Set Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-12-27 16:59 +0000
          Re: Compute Unique Numbers in a Set Richard Damon <Richard@Damon-Family.org> - 2022-12-27 12:24 -0500
            Re: Compute Unique Numbers in a Set Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-12-27 17:53 +0000
              Re: Compute Unique Numbers in a Set Richard Damon <Richard@Damon-Family.org> - 2022-12-27 13:50 -0500
                Re: Compute Unique Numbers in a Set Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-12-27 20:08 +0000
                Re: Compute Unique Numbers in a Set Richard Damon <Richard@Damon-Family.org> - 2022-12-27 15:31 -0500
                Re: Compute Unique Numbers in a Set Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-12-28 02:57 +0000
                Re: Compute Unique Numbers in a Set Richard Damon <Richard@Damon-Family.org> - 2022-12-27 23:02 -0500
                Re: Compute Unique Numbers in a Set Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-12-29 02:06 +0000
                Re: Compute Unique Numbers in a Set Richard Damon <Richard@Damon-Family.org> - 2022-12-28 23:42 -0500
                Re: Compute Unique Numbers in a Set Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-12-29 12:26 +0000
  Re: Compute Unique Numbers in a Set Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-12-27 07:34 -0800
  Re: Compute Unique Numbers in a Set Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-12-27 16:18 +0000
    Re: Compute Unique Numbers in a Set Mike Terry <news.dead.person.stones@darjeeling.plus.com> - 2022-12-28 01:08 +0000
      Re: Compute Unique Numbers in a Set Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-12-28 03:30 +0000
    Re: Compute Unique Numbers in a Set Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-12-27 19:42 -0800
  Re: Compute Unique Numbers in a Set Manu Raju <MR@invalid.invalid> - 2022-12-27 18:11 +0000
  Re: Compute Unique Numbers in a Set antispam@math.uni.wroc.pl - 2022-12-28 01:32 +0000
    Re: Compute Unique Numbers in a Set Richard Damon <Richard@Damon-Family.org> - 2022-12-27 21:13 -0500
      Re: Compute Unique Numbers in a Set Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-12-27 19:48 -0800
        Re: Compute Unique Numbers in a Set Richard Damon <Richard@Damon-Family.org> - 2022-12-27 23:06 -0500
      Re: Compute Unique Numbers in a Set antispam@math.uni.wroc.pl - 2022-12-29 19:47 +0000
  Re: Compute Unique Numbers in a Set jak <nospam@please.ty> - 2022-12-28 11:28 +0100
  Re: Compute Unique Numbers in a Set Rosario19 <Ros@invalid.invalid> - 2023-01-01 21:06 +0100
    Re: Compute Unique Numbers in a Set Rosario19 <Ros@invalid.invalid> - 2023-01-02 06:43 +0100
  Re: Compute Unique Numbers in a Set gazelle@shell.xmission.com (Kenny McCormack) - 2023-01-01 23:19 +0000
    Re: Compute Unique Numbers in a Set jak <nospam@please.ty> - 2023-01-02 07:28 +0100
      Re: Compute Unique Numbers in a Set jak <nospam@please.ty> - 2023-01-02 08:48 +0100
      Re: Compute Unique Numbers in a Set Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-01-01 23:53 -0800
        Re: Compute Unique Numbers in a Set Öö Tiib <ootiib@hot.ee> - 2023-01-02 01:18 -0800
    Re: Compute Unique Numbers in a Set gazelle@shell.xmission.com (Kenny McCormack) - 2023-01-02 13:49 +0000
  Re: Compute Unique Numbers in a Set Bart <bc@freeuk.com> - 2023-01-02 12:27 +0000
  Re: Compute Unique Numbers in a Set Richard Damon <Richard@Damon-Family.org> - 2023-01-02 12:13 -0500
    Re: Compute Unique Numbers in a Set Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-01-02 17:31 +0000
      Re: Compute Unique Numbers in a Set Richard Damon <Richard@Damon-Family.org> - 2023-01-02 12:46 -0500
      Re: Compute Unique Numbers in a Set Siri Cruise <chine.bleu@yahoo.com> - 2023-01-02 18:54 -0800
      Re: Compute Unique Numbers in a Set Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-01-02 20:52 -0800
      Re: Compute Unique Numbers in a Set David Brown <david.brown@hesbynett.no> - 2023-01-03 09:01 +0100
      Re: Compute Unique Numbers in a Set Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-01-03 07:28 -0800
        Re: Compute Unique Numbers in a Set gazelle@shell.xmission.com (Kenny McCormack) - 2023-01-03 15:46 +0000
          Re: Compute Unique Numbers in a Set David Brown <david.brown@hesbynett.no> - 2023-01-03 18:19 +0100
  Re: Compute Unique Numbers in a Set Bonita Montero <Bonita.Montero@gmail.com> - 2023-01-08 03:48 +0100
    Re: Compute Unique Numbers in a Set Bonita Montero <Bonita.Montero@gmail.com> - 2023-01-08 04:18 +0100
    Re: Compute Unique Numbers in a Set gazelle@shell.xmission.com (Kenny McCormack) - 2023-01-08 03:48 +0000
      Re: Compute Unique Numbers in a Set Bonita Montero <Bonita.Montero@gmail.com> - 2023-01-08 05:12 +0100
        Re: Compute Unique Numbers in a Set Bonita Montero <Bonita.Montero@gmail.com> - 2023-01-08 06:01 +0100
          Re: Compute Unique Numbers in a Set Bart <bc@freeuk.com> - 2023-01-08 14:48 +0000
            Re: Compute Unique Numbers in a Set Bonita Montero <Bonita.Montero@gmail.com> - 2023-01-08 18:22 +0100
              Re: Compute Unique Numbers in a Set Bart <bc@freeuk.com> - 2023-01-08 17:46 +0000
                Re: Compute Unique Numbers in a Set Bonita Montero <Bonita.Montero@gmail.com> - 2023-01-09 04:58 +0100
                Re: Compute Unique Numbers in a Set Bart <bc@freeuk.com> - 2023-01-09 11:26 +0000
                Re: Compute Unique Numbers in a Set Bonita Montero <Bonita.Montero@gmail.com> - 2023-01-09 15:57 +0100
            Re: Compute Unique Numbers in a Set Bart <bc@freeuk.com> - 2023-01-08 17:34 +0000
              Re: Compute Unique Numbers in a Set Ike Naar <ike@sdf.org> - 2023-01-08 21:45 +0000
                Re: Compute Unique Numbers in a Set Bart <bc@freeuk.com> - 2023-01-08 23:13 +0000
                Re: Compute Unique Numbers in a Set "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-01-08 15:18 -0800
          Re: Compute Unique Numbers in a Set Paavo Helde <eesnimi@osa.pri.ee> - 2023-01-08 21:19 +0200
          Re: Compute Unique Numbers in a Set "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2023-01-09 12:03 +0100
            Re: Compute Unique Numbers in a Set Bonita Montero <Bonita.Montero@gmail.com> - 2023-01-09 17:42 +0100
              Re: Compute Unique Numbers in a Set Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-01-09 14:48 -0800
              Re: Compute Unique Numbers in a Set Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-01-09 23:22 +0000
                Re: Compute Unique Numbers in a Set Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-01-09 18:28 -0800
                Re: Compute Unique Numbers in a Set Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-01-09 18:44 -0800
                Re: Compute Unique Numbers in a Set Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-01-10 03:08 +0000
                Re: Compute Unique Numbers in a Set Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-01-09 19:19 -0800
                Re: Compute Unique Numbers in a Set Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-01-10 17:30 +0000
                Re: Compute Unique Numbers in a Set Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-01-10 09:45 -0800
                Re: Compute Unique Numbers in a Set Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-01-10 02:57 +0000
              Re: Compute Unique Numbers in a Set Bonita Montero <Bonita.Montero@gmail.com> - 2023-01-13 08:26 +0100
                Re: Compute Unique Numbers in a Set Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-01-13 03:32 -0800
                Re: Compute Unique Numbers in a Set gazelle@shell.xmission.com (Kenny McCormack) - 2023-01-13 12:21 +0000
                Re: Compute Unique Numbers in a Set Bonita Montero <Bonita.Montero@gmail.com> - 2023-01-13 14:11 +0100
                Re: Compute Unique Numbers in a Set gazelle@shell.xmission.com (Kenny McCormack) - 2023-01-13 13:55 +0000
                Re: Compute Unique Numbers in a Set Bonita Montero <Bonita.Montero@gmail.com> - 2023-01-13 15:02 +0100
                Re: Compute Unique Numbers in a Set gazelle@shell.xmission.com (Kenny McCormack) - 2023-01-13 14:17 +0000
                Re: Compute Unique Numbers in a Set Bonita Montero <Bonita.Montero@gmail.com> - 2023-01-15 16:06 +0100
                Re: Compute Unique Numbers in a Set Bart <bc@freeuk.com> - 2023-01-15 16:27 +0000
                Re: Compute Unique Numbers in a Set Bonita Montero <Bonita.Montero@gmail.com> - 2023-01-15 17:42 +0100
                Re: Compute Unique Numbers in a Set gazelle@shell.xmission.com (Kenny McCormack) - 2023-01-15 17:11 +0000
        Re: Compute Unique Numbers in a Set tTh <tth@none.invalid> - 2023-01-08 10:13 +0100
          Re: Compute Unique Numbers in a Set Bonita Montero <Bonita.Montero@gmail.com> - 2023-01-08 10:25 +0100
            Re: Compute Unique Numbers in a Set gazelle@shell.xmission.com (Kenny McCormack) - 2023-01-08 13:20 +0000
    Re: Compute Unique Numbers in a Set "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-01-08 13:09 -0800
  Re: Compute Unique Numbers in a Set Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-01-09 02:37 +0000
  Re: Compute Unique Numbers in a Set John Forkosh <forkosh@panix.com> - 2023-01-15 02:49 +0000

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