Radix sort

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The Radix sort is an integer sorting algorithm.

Features

• Very fast

unit URadixSort.pas

unit URadixSort;

{$mode objfpc}{$H+}

interface

uses
  Classes, SysUtils, 
  GQueue ; //  packages/fcl-stl/src/gqueue.pp

type
  // data type
  TItemRadixSort=integer;

// sorting function
procedure RadixSort( var a: array of TItemRadixSort );

implementation



procedure RadixSort( var a: array of TItemRadixSort );

const
  BASE = 16;

type TQueueIRS = specialize TQueue< TItemRadixSort >;

var
  jono : array[ 0 .. BASE - 1 ] of TQueueIRS;
  max : TItemRadixSort;
  i ,k : integer;

  procedure pick;
  var
    i, j: integer;
  begin
    i := 0;
    j := 0;
    while i < high( a ) do
      begin
         while not jono[ j ].IsEmpty do
           begin
             a[ i ] := jono[ j ].Front;
             jono[ j ].Pop;
             inc( i );
           end;
         inc( j );
      end;
  end;

begin
  max := high( a );
  for i := 0 to BASE - 1 do
    jono[ i ] := TQueueIRS.Create;
  for i := low( a ) to high( a ) do
    begin
      if a[ i ] > max then max := a[ i ];
      jono[ abs( a[ i ] mod BASE ) ].Push( a[ i ] );
    end;
  pick;
  k := BASE;
  while  max > k do
    begin
      for i := low( a ) to high( a ) do
        jono[ abs( a[ i ] div k mod BASE ) ].Push( a[ i ] );
      pick;
      k := k * BASE;
    end;
  for i := 0 to BASE - 1 do
    jono[ i ].Free;

end;

end.

Example of the use

uses
  URadixSort

  ...

var

  a: array[0..100] of integer; 


begin

  ...

  RadixSort( a );