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<center><h2>cs150: Notes 10</h2></center>

<h4>Assignments Due</h4>


<ul>
<li> <b>Monday, 12 February</b> (beginning of class): <a
href="/cs150/ps/ps3/">Problem Set 3</a>
</ul>

<h4>Lab Hours</h4>

Kinga's lab hours tomorrow will be 4-5:30pm, instead of the normally
scheduled 6-7:30pm time.  Richard will have his normal lab hours tomorrow,
7:30-9pm.  This afternoon, Dan will have his normal lab hours, 4-5:30pm.
<p>
Please take advantage of the scheduled lab hours to make progress on
PS3.

<h4>Pegboard Puzzle</h4>

First, we need a way to represent the state of a board.  The way we use
is a bit strange, but will make solving the problem easier.  Instead of
keeping a list of the pegs, we keep a list of the empty squares.  If a
valid board position is not in the list of empty squares, it means there
is a peg at that position.

<pre>
;;; A board is a pair of the number of rows and the empty squares
(define (make-board rows holes) (cons rows holes))
(define (board-holes board) (cdr board))
(define (board-rows board) (car board))

;;; A position is a pair of a row and column.
;;;
;;; make-position creates an row, col coordinate that 
;;; represents a position on the board
;;; e.g.             1,1
;;;               2,1   2,2
;;;            3,1   3,2   3,3
(define (make-position row col) (cons row col))
(define (get-row posn) (car posn))
(define (get-col posn) (cdr posn))

(define (same-position pos1 pos2)
  (and (= (get-row pos1) (get-row pos2))
       (= (get-col pos1) (get-col pos2))))
</pre>
Define a procedure <tt>on-board?</tt> that takes as inputs a board and a
position, and outputs true if and only if the position is on the board.
<pre>






</pre>

Define a procedure <tt>remove-peg</tt> that takes as input a board and a
position, and produces as output the board with the peg at the input
positition removed.
<pre>
(define (remove-peg board posn)
  (make-board (board-rows board) 

              _______________________))
</pre>

Define a procedure <tt>add-peg</tt> that takes as input a board and a
position, and produces as output the board with a peg added at the input
positition.  (Hint: this is much tougher.)
<pre>







</pre>
Next, try to solve as much of the problem as you can.  You should first
think about how to simulate a jump on the board.  Then, consider how to
find all the possible jumps on a given board.  Finally, consider how to
search all the possible sequences of jumps to find a winning sequence.  
<p>
Good luck!  And remember, even if you leave two pegs, "you're purty smart".
<p>
<center><img src="cb-small.jpg" width=320 height=240></center>
<p>

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