Question

Towers of Hanoi non recursive solution

Asked by: ognianbg

I want  to write a program that solves the puzzle of the hanoi towers without using recursion. I think I understand the recursive
version but I don't know how to convert it into a non recursive one.
PROGRAM Hanoi(input, output);
VAR N:integer;
PROCEDURE dohanoi(N, Tfrom, Tto, Tusing : integer);
  BEGIN
   if N > 0 THEN
       BEGIN dohanoi(N-1, Tfrom, Tusing, Tto);
       writeln('move ', Tfrom:1, ' --> ', Tto:1);
       dohanoi(N-1, Tusing, Tto, Tfrom);
       END END;
 BEGIN write('N = ? '); r
 eadln(N);
 writeln;
 dohanoi(N, 1, 3, 2)
END.  


So the formula for finding the number of steps it takes to transfer N disks from post A to post B is: 2^n - 1.
I'll be glad if you can provide me with some links where I can find the program I'm looking for or paste the code itself. Or perhaps
give me some instructions because I don't have any ideas for solving the problem. Thank you in advance.

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Asked On
2003-05-28 at 06:40:58ID20628825
Tags

hanoi

,

recursive

Topic

Pascal Programming Language

Participating Experts
1
Points
75
Comments
3

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Answers

 

by: OkeyPosted on 2003-05-28 at 21:29:34ID: 8603304

To Roll a Recursion do the following!
- Globalize your Variables (No Lokal Variables or useage of PARAMETERS)
- Instead of doing a recursive call try  to handle it in loops!
SN:=N;
  while N > 0 THEN
   BEGIN
        N:=N-1,
        writeln('move ', Tfrom:1, ' --> ', Tto:1);  
{Exchange the variables like your recursion would repeatedly do}
    Tusing:=TTo-TUsing;
     TTO:=TUSING+TTO;
     TUSING:=TTO+TUsing;
   END
 ...
 Then Exchange repeatedly the Variables like Your recursion would do, after your recursive calls are done.
 
  N:=SN;
  while N > 0 THEN
   BEGIN
        N:=N-1,
        writeln('move ', Tfrom:1, ' --> ', Tto:1);  
{Exchange the variables like your recursion would repeatedly do}
       Tusing:=TFrom-TUsing;
       TFrom:=TUSING+TFrom;
       TUSING:=TFrom+TUsing;
   END
 ...
 I think that's it, but your recursion was nicer and none the less by stack limited!
Perfect example whatfor a recursion is thought!!

 

by: ognianbgPosted on 2003-05-29 at 14:32:22ID: 8609281

Thank you very much for your help Okey but there seems to be something wrong with the implementation of the above code. This is the program I wrote
using your hints:
program MyHanoi;
{$APPTYPE CONSOLE}
uses
  SysUtils;

var N, Tusing, TTo, Tfrom, SN:integer;
begin
SN:=N;
 while N > 0 DO
   BEGIN
        N:=N-1;
        writeln('move ', Tfrom:1, ' --> ', Tto:1);
{Exchange the variables like your recursion would repeatedly do}
   Tusing:=TTo-TUsing;
    TTO:=TUSING+TTO;
    TUSING:=TTO+TUsing;
  END;
  N:=SN;
 while N > 0 DO
   BEGIN
        N:=N-1;
        writeln('move ', Tfrom:1, ' --> ', Tto:1);  
{Exchange the variables like your recursion would repeatedly do}
      Tusing:=TFrom-TUsing;
      TFrom:=TUSING+TFrom;
      TUSING:=TFrom+TUsing;
  END;
readln
end.

It gives the following result:
move 1 --> 3
move 1 --> 4
move 1 --> 3
move 1 --> 4
move -3 -->4
move 1 --> 4

I can;t figure out what am I doing wrong?

 

by: OkeyPosted on 2003-05-29 at 16:12:21ID: 8609764

Oh I'm sorry but this shouldn't be the sollution, just still an Idea how I would do such things!

I didn't  solute it completely, I just gave you a Hint!

So try to write a program that will do the right output and don't think aboiut a short recursion to achieve your aim.
Try to solute it by using loops!

Else You can do following trick!
Save all parameters for the recursion in an array!
Now you needn't call recursive,
you just work your listing down like your recursion would do it on stack!

This leads to ugly but non recursive code with loop and if-then-else statements!

N seems to be then the index of your recursive parameter array/list!

20120131-EE-VQP-002

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