Re: [Haskell-beginners] tower hanoi problem

Um ... To the other people giving hints: Don't forget that in the sequence *of lines in the program* you have to state the base case(s) *first*, certainly in Haskell, which goes through the lines in order, until it finds a match. That's what I meant when I said "first do the base case(s), then the rest": first *in the program order*, if not necessarily in the conceptual structure. So for the depth-first binary tree which Joel Neely pointed out, *first* you must deal with the base case that the node being looked at is actually a leaf; *only then* can you deal with the fact that in general the algorithm has the structure <process left descendants><process this node><process right descendants>. So if you try <move stack off of bottom><move bottom><place stack on bottom>, the first part will either enter an endless loop or will generate an error, because it doesn't have a base case. (No pun on "base" intended.) On 2/17/15 4:05 AM, Joel Neely wrote:

​Let's tweak your answers​ just a bit, calling the three pegs the "source", "goal", and "spare" pegs:

On Tue, Feb 17, 2015 at 5:23 AM, Roelof Wobben mailto:r.wobben@home.nl> wrote:

- Where do I move the bottom (largest disk) ?

To the last peg, which do not contain any disk then ​ .

From the source peg to the goal peg, which will /must not contain any disks.​

​

- What must happen before I can move the bottom disk ?

I have to move the disk which above that disk.

Move everything else from ____ to ____.​

- What must happen after I move the bottom disk ?

All the other disk must be placed above that disk.

​ Move everything else from ____ to ____.​

​So more questions/hints:

1. How do you fill in the blanks? 2. How do you put the three statements in order? 3. How many disks does each statement talk about?

-jn- ​

-- Beauty of style and harmony and grace and good rhythm depend on simplicity. - Plato

_______________________________________________ Beginners mailing list Beginners@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners