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Larry's Winning Checker

Welcome to Larry's Winning Checker on Exercism's Common Lisp Track. If you need help running the tests or submitting your code, check out HELP.md. If you get stuck on the exercise, check out HINTS.md, but try and solve it without using those first :)

Introduction

Arrays

In Common Lisp like other languages an array is a set of elements which are accessed via integral indexes. The types of the elements can be heterogeneous. The array can be multi-dimensional (not simply 1-dimensional).

Creating

make-array allows one to create arrays. It has many options but its simpler forms allow one to create N-dimensional arrays with all elements initialized to a single value or the array initialized to the values in another sequence (such as a list). Its first argument is a list of the size of each dimension.

(make-array '(4) :initial-element 3)    ; => #(3 3 3 3)
(make-array '(2 2) :initial-element 'x) ; => #2A((X X) (X X))

(Notice how the N-dimensional arrays are printed with the number of dimensions.)

Arrays can also be created by using the same format they are printed in:

#(x y z)         ; => #(X Y Z)
#2A((1 2) (3 4)) ; => #2A((1 2) (3 4))

Accessing Elements

To access elements of a vector use aref, the indexes are zero-based. The number of indexes provided must match the rank of the array.

(aref #2A((1 2 3) (3 4 5)) 
       1 0)           ; => 3
(aref #3A(((a b) (c d)) 
           ((e f) (g h)) 
           ((t u) (v w))) 
       2 0 1)         ; => U
(aref #2A((1) (2)) 0) ; => ERROR (because not enough indexes provided)

Instructions

Larry is a Lisp Alien that likes to write code to play games. Today they want to write a few functions to help them with a game which is a lot like tic-tac-toe.

Like tic-tac-toe this game is played on a board which is a 3x3 grid.

1. Starting from scratch

First Larry needs a function to make a blank board make-empty-board All the cells of the board should be NIL.

(make-empty-board) ; => #2A((NIL NIL NIL) (NIL NIL NIL) (NIL NIL NIL))

2. Starting from an existing board

Next Larry needs a function to make a board from a list of rows. For example:

(make-board-from-list '((A B C) (D E F) (G H I))) ; => #2A((A B C) (D E F) (G H I))

3. Winning condition

If there is a case where there are 3 of the same symbol in a row then that player has won. Larry will need a function, all-the-same-p, which given an array of 3 items will evaluate to T if all the items are the same symbol. (eq can be used to determine if two symbols are the same.)

(all-the-same-p #(A A A)) ; => T
(all-the-same-p #(A B C)) ; => NIL

4. In a row

Now Larry needs a way to get the elements of a row. The function row will take a board and a row number and should return an array of the elements in that row.

(row #2A((1 2 3) (4 5 6) (7 8 9)) 1) ; => #(4 5 6)

5. In a column

Finally Larry needs a way to get the elements of a column. The function column will take a board and a column number and should return an array of the elements in that column.

(column #2A((1 2 3) (4 5 6) (7 8 9)) 1) ; => #(2 5 8)

Source

Created by

  • @verdammelt

My Solution