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***drdebcol*** · 07-26-2009, 08:48 PM

This is a bit advanced algorithm for permutations of elements. It writes in file elements which you specified ! It uses recursive algorithm :

Code:

program permutations_of_elements;

uses wincrt;

 var

  a:array[1..100] of integer;

  i,n:integer;

  s:array[1..100] of char;

  out:text;

  location:string;

procedure output;

 var

  i:integer;

begin 

 for i:=1 to n do

  write(out,s[a[i]]);

 writeln(out);

end;

function check(k:integer):boolean;

 var

  i:integer;

  b:boolean;

begin

  b:=false;

  for i:=1 to k-1 do

    if b=false then

      if a[i]=a[k] then

        b:=true;

 if b=true then

   check:=false

 else

   check:=true;

end;

procedure recursion(index:integer);

 var

   i:integer;

begin

  if index>n then

    output

  else

    begin

     for i:=1 to n do

      begin

       a[index]:=i;

        if check(index) then     

          recursion(index+1);

       end;

    end;

end;

begin

writeln('Program for writing permutations');

writeln('of n elements in a specified file !');

writeln('How much elements (chars) do you want ?');

readln(n);

for i:=1 to n do

 begin

  write(i,' = ');

  readln(s[i]);

end;

writeln('Enter location of output file ?');

readln(location);

assign(out,location);

rewrite(out);

recursion(1);

writeln('Process completed !');

close(out);

end.

***Back_track*** · 07-27-2009, 03:31 AM

Impressive yet another algorithm that makes good use of recursion!

***drdebcol*** · (This post was last modified: 07-27-2009 06:09 AM by drdebcol.)

(07-27-2009 03:31 AM)Back_track Wrote: Impressive yet another algorithm that makes good use of recursion!

Yeah it basically tries every possible combination with class n !
And then checks if one number was used before, and if it is, it brakes that process and goes to another until it gets n different numbers in array, and then
it just writes char array in order of integer array !
Number of permutations = factorial(n) .
n ! = 1*2*3*...*n

BTW This is 700th post on this forum !