[SUMMARY] Sliding Puzzle (#196)

The sole submission to this week's quiz comes from Martin Boese.
Martin provided a simple and versatile solution. It can generate
puzzles of any size, and is able to shuffle to a random starting
configuration. It also throws a nice party when the player succeeds.

The program provides a driver that reads keyboard commands and
translates them into the correct actions on the puzzle class. The
program accepts four movement commands as well as commands to quit and
shuffle.

Here's a look at the puzzle's shuffle method to randomize the configuration:

    def shuffle
      100.times { move 'udlr'[(rand*4).to_i].chr }
    end

The shuffling is done by making 100 random moves, this ensures that
the puzzle remains solvable; a random shuffling of the tiles without
maintaining the movement constraints is not necessarily solvable.
Additionally, this leverages the existing functionality of the `move`
method to keep the code simple. One potential drawback is that this
doesn't select all possible starting positions with equal probability.
However, having the random configurations generated with equal
probability wasn't a quiz requirement, and it is often best to go with
the least complex solution that meets the requirements.

The method to detect whether or not the puzzle is solved also
leverages existing functionality to reduce complexity, it checks if
the current board is equal to a newly created board. Because the newly
created board starts in the solved position and the board is an array
of integers, this leads to a short and sweet definition:

    def solved?
      @board == mkboard(@x,@y) && @moved
    end

The check for `@moved` to be true is to prevent the puzzle from
partying when the game is first created and before it is shuffled.
Speaking of the party, here's the section responsible for that magical
functionality:

    puts
    10.times { $stdout.print '*'; sleep 0.1; $stdout.flush }
    puts " You won!\n"

It creates a rapid display of asterisks and congratulates the player!

Thank you, Martin, for a wonderful solution!

http://rubyquiz.strd6.com/quizzes/196

- Daniel