15 puzzle game

Most of this is interface code. Reused substantial portions from the 2048 task. Use the arrow keys to slide tiles, press 'q' to quit or 'n' for a new puzzle. Requires a POSIX termios aware terminal. Ensures that the puzzle is solvable by shuffling the board with an even number of swaps, then checking for even taxicab parity for the empty space.

use Term::termios;

constant $saved   = Term::termios.new(fd => 1).getattr;
constant $termios = Term::termios.new(fd => 1).getattr;
# raw mode interferes with carriage returns, so
# set flags needed to emulate it manually
$termios.unset_iflags(<BRKINT ICRNL ISTRIP IXON>);
$termios.unset_lflags(< ECHO ICANON IEXTEN ISIG>);
$termios.setattr(:DRAIN);

# reset terminal to original setting on exit
END { $saved.setattr(:NOW) }

constant n    = 4; # board size
constant cell = 6; # cell width

constant $top = join '─' x cell, '┌', '┬' xx n-1, '┐';
constant $mid = join '─' x cell, '├', '┼' xx n-1, '┤';
constant $bot = join '─' x cell, '└', '┴' xx n-1, '┘';

my %dir = (
   "\e[A" => 'up',
   "\e[B" => 'down',
   "\e[C" => 'right',
   "\e[D" => 'left',
);

my @solved = [1,2,3,4],[5,6,7,8],[9,10,11,12],[13,14,15,' '];
my @board;
new();

sub new () {
    loop {
       @board = shuffle();
       last if parity-ok(@board);
   }
}

sub parity-ok (@b) {
    my $row = @b.first(/' '/,:k);
    my $col = @b[$row].first(/' '/,:k);
    so ([3,3] <<->> [$row,$col]).sum %% 2;
}

sub shuffle () {
    my @c = [1,2,3,4],[5,6,7,8],[9,10,11,12],[13,14,15,' '];
    for (^16).pick(*) -> $y, $x {
        my ($yd, $ym, $xd, $xm) = ($y div n, $y mod n, $x div n, $x mod n);
        @(@c[$ym;$yd],@c[$xm;$xd]) = @(@c[$xm;$xd],@c[$ym;$yd]);
    }
    @c;
}

sub row (@row) { '│' ~ (join '│', @row».&center) ~ '│' }

sub center ($s){
    my $c   = cell - $s.chars;
    my $pad = ' ' x ceiling($c/2);
    sprintf "%{cell}s", "$s$pad";
}

sub draw-board {
    run('clear');
    print qq:to/END/;


	Press direction arrows to move.

	Press q to quit. Press n for a new puzzle.

	$top
	{ join "\n\t$mid\n\t", map { .&row }, @board }
	$bot

	{ (so @board ~~ @solved) ?? 'Solved!!' !! '' }
END
}

sub slide (@c is copy) {
    my $t = (grep { /' '/ }, :k, @c)[0];
    return @c unless $t and $t > 0;
    @c[$t,$t-1] = @c[$t-1,$t];
    @c;
}

proto sub move (|) {*};

multi move('up') {
    map { @board[*;$_] = reverse slide reverse @board[*;$_] }, ^n;
}

multi move('down') {
    map { @board[*;$_] = slide @board[*;$_] }, ^n;
}

multi move('left') {
    map { @board[$_] = reverse slide reverse @board[$_] }, ^n;
}

multi move('right') {
    map { @board[$_] = slide @board[$_] }, ^n;
}

loop {
    draw-board;

    # Read up to 4 bytes from keyboard buffer.
    # Page navigation keys are 3-4 bytes each.
    # Specifically, arrow keys are 3.
    my $key = $*IN.read(4).decode;

    move %dir{$key} if so %dir{$key};
    last if $key eq 'q'; # (q)uit
    new() if $key eq 'n';
}

Sample screen shot:

        Press direction arrows to move.

        Press q to quit. Press n for a new puzzle.

        ┌──────┬──────┬──────┬──────┐
        │  2   │  1   │  10  │  14  │
        ├──────┼──────┼──────┼──────┤
        │  15  │  11  │  12  │      │
        ├──────┼──────┼──────┼──────┤
        │  13  │  3   │  6   │  7   │
        ├──────┼──────┼──────┼──────┤
        │  9   │  4   │  5   │  8   │
        └──────┴──────┴──────┴──────┘