I am confused with concept of recursion ...help plz

Question

Hi all,
I am bit confused with the concept of recursion. I am looking for a good online resource
to learn more about it. If anyone knows abt it and recommend, i 'd be grateful.
abdul

Answer 1

Recursion is no more no less than the decomposition of a problem into smaller parts
that happen to be identical to the original problem but just smaller. Finally, the
decompostion boils down to a trivial problem. Allow me to give you an example:
The towers of Hanoi problem is defined as follows: far away in a monastry in
Hanoi, monks face the following puzzle: there are three large poles, next to each
other,erected vertically. The leftmost pole is populated with 64 millstone disks
(round with a whole in the centre). The smallest disk is on top, the next disk
is below the smallest disk etc. while the largest disk resides at the bottom.
The monks have to transfer this 'tower' to the rightmost pole, one disk at the
time. There is just one rule: no larger disk may be placed on top of a smaller disk
and all three poles may be used for placing disks on them.
The question is: how to solver this problem? Recursion is your friend here.
Here's the recursive reasoning: suppose you are able to transfer the entire
tower (except the largest disk at the bottom) to the middle pole. Then you
can transfer the largest disk to the rightmost pole and you ask yourself again
to transfer that 'sub' tower (situated at the middle pole) to the rightmost pole.
(read this again and again ;) This efffectively solves the puzzle. Of course,
(and this is the trivial part) when there are no disks to transfer, nothing has
to be done.
Here's some pseudo code that implements the reasoning above:
   void Hanoi(Pole left, Pole mid, Pole right, int size) {
      if (size > 0) { // anything to do?
         Hanoi(left, right, mid, size-1); // move 'sub' tower to the middle pole
         System.out.println("from "+left+" to "+right); // move the disk
         Hanoi(mid, left,  right, size-1); // move from the mid pole to the right
   }Are you dizzy yet? ;-)
kind regards
ps. Blaim any typos to the sun; I'm typing this in my garden, using a wireless connection from my
little laptop. Call me a happy camper ;-)