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The Tower of Hanoi problem

Posted on 1998-03-10
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Last Modified: 2013-12-26
I need to write a shell script on a Sun system in K-shell that solves the Tower of Hanoi Problem.  It must use a recursive function.  I'm stumped.  

Sorry, perhaps I should have elaborated.  I have a sample program written out for this problem.  I have the function already set up and it does call itself.  The problem lies in the fact that it doesn't move the disks in the right order.
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Question by:KCMSzwak
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by:q2guo
ID: 1296111
most of the recursive function can be replaced by using loops.
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by:jhance
ID: 1296112
Sounds like a homework problem.  How about a hint?

The k-shell provides for function definitions.  So in your script you can define one like:

function blah
{
   # Do some stuff
}

So it follows that you can have blah call itself recursively:

function blah
{
  # Do some stuff
  blah

  # Do some more stuff
}

Don't forget that somewhere you have to test whether blah needs to be called again.  Otherwise, you'll just keep calling blah until the computer's memory runs out.
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by:KCMSzwak
ID: 1296113
Edited text of question
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by:jhance
ID: 1296114
Obviously you've programmed it wrong.  Program it correctly and it's likely to work.  From what you've posted, I don't see that any more definitive help is possible.
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by:jos010697
ID: 1296115
Show me your code and I'll try to fix it (I know next to nothing about the ksh, so
I need your syntax first ;-) In pseudo code:

# from, to == 1, 2, 3, size >= 0
function Hanoi(from, to, size) {

   if (size) {
      Hanoi(from, 6-from-to, size-1);
      move(from, to);
      Hanoi(6-from-to, to, size-1);
   }

kind regards,

Jos aka jos@and.nl

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Expert Comment

by:dps96r
ID: 1296116
There are also a range of non-recursive solutions to the towers
of hanoi problem. A stack should not be too hard to improvise if
the syntsx is something close to a bourne shell--just use a stack
pointer (i.e. counter) and eval to get the right number of levels
of shell expansion. This probably leaves some values around but
unset fixes that if you want the fineese. [I would be unlikely to
bother myself].
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Accepted Solution

by:
shivak earned 50 total points
ID: 1296117
#!/bin/ksh

# A recurssive function to perform the moves
hanoi()
{
    if [ $1 -ne 0 ]
    then
        hanoi `expr $1 - 1` $2 $4 $3
        echo "Move disk $1 from peg $2 to peg $3"
        hanoi `expr $1 - 1` $4 $3 $2
    fi
}


#main program
echo "Enter the number of disks :"
read x
if [ "$x" -ge 0 ]
then
    # Call hanoi to move N disks from peg A to peg C
    # using peg B
    hanoi $x A C B
else
    echo Its invalid
fi 2>/dev/null

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