Challenge: Fastest Unique Random Number Generator

Delphi Challenge: Fill an Integer Array with Unique Random Numbers

Delphi programming challenges / exercises are designed to help you refactor your old code to make it more efficient; get new ideas on how to code faster / better Delphi code; help you solve a particular Delphi programming task and of course: to have fun while coding in Delphi :)

Challenge: Fastest Unique Random Number Generator

Your challenge is to code a custom Delphi procedure with the following signature:

procedure Randomizer(const maxValue : int64; var values : array of int64) ;

Randomizer takes 2 parameters: values is an int64 open array. Your code must fill in the "values" array with unique random numbers from 1 to maxValue.

For example, if maxValue is 10 and the length of the array is 5,
a valid entry would be [2,3,1,8,7]
a non - valid entry is [2,4,6,4,10] - two 4's.

The following code should be used to prepare the array and call the Randomizer procedure:

uses Math;

const
  sizeExponent = 2; // 1 or 3 or 4 or 5 or ...
var
  arraySize : int64;
  maxValue : int64;
  values : array of int64;
begin
  arraySize := Trunc(Power(10, sizeExponent)) ;
  maxValue := 10 * arraySize;
  SetLength(values, arraySize) ;

  Randomizer(maxValue, values) ;

  // "values" array should be filled with
  // unique random numbers from 1 to maxValue
end;

Here are a few hints:

• Understanding and Using Array data types in Delphi
• High function
• Generating random numbers

Accepted Entries (so far)

Here's the list of the accepted entries. 14 entries were accepted before initial results were published.

Note: the list is in the order of execution speed, with the best results on top.

99 microseconds by Patrick van Logchem
WINNER - 10 "fame and glory" points! :)

Hrvoje Brozović - 353 microseconds
David Reed - 370 microseconds
Kaushalya Damitha Weerakoon - 860 microseconds
Peter Kras - 3300 microseconds
Jim Murtha - 3 600 microseconds
Stefan Tashev - 6150 microseconds
Jim McKeeth - 125 milliseconds
Marius van Loo - 130 milliseconds
Willie Geldenhuys - 130 milliseconds
Didier Cabalé - 350 milliseconds
Harry Stockx - 400 milliseconds
Dorin Duminica - 625 milliseconds
Korhan Taþçýkar - 3 seconds

Note: test are done on a Pentium 2.4, 2GM RAM machine with Windows XP Pro installed.

To test the speed of execution the TStopWatch - High Precision Timer class was used.

Challenge CLOSED

Note: this challenge is closed. Several valid entries have been submitted before the challenge was closed and the winner(s) announced.

Delphi programming challenges / exercises are designed to help you refactor your old code to make it more efficient; get new ideas on how to code faster / better Delphi code; help you solve a particular Delphi programming task and of course: to have fun while coding in Delphi :)

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