Advent Calendar 2021
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The gift is presented by Luca Ferrari. Today he is talking about his solution to “The Weekly Challenge - 126”. This is re-produced for Advent Calendar 2021 from the original post by Luca Ferrari.
Task #2: Minesweeper Game
You are given a rectangle with points marked with either x or *. Please consider the x as a land mine.
Write a script to print a rectangle with numbers and x as in the Minesweeper game.
Example
Input:
x * * * x * x x x x
* * * * * * * * * x
* * * * x * x * x *
* * * x x * * * * *
x * * * x * * * * x
Output:
x 1 0 1 x 2 x x x x
1 1 0 2 2 4 3 5 5 x
0 0 1 3 x 3 x 2 x 2
1 1 1 x x 4 1 2 2 2
x 1 1 3 x 2 0 0 1 x
The second task was about rewriting the mine swiper game. The task was not hard, but I solved with a few nested loops. First of all, let’s do a couple of utility functions:
is-mine accepts the array of input and the position (as row and column), and returns true if the position is a mine (i.e., an x);
compute-mines accepts the same input and tries to move on near positions to see how many mines there are.
sub is-mine( @input, $row, $column ) {
return @input[ $row ][ $column ] ~~ 'x';
}
sub compute-mines( @input, $row, $column ) {
my $counter = 0;
# see where we can move
my ( $can-left, $can-right, $can-up, $can-down ) =
$column > 0, $column < @input[ 0 ].elems, $row > 0, $row < @input.elems;
# left, if possible
$counter++ if ( $can-left && is-mine( @input, $row, $column - 1 ) );
# up if possible
$counter++ if ( $can-up && is-mine( @input, $row - 1, $column ) );
# down if possible
$counter++ if ( $can-down && is-mine( @input, $row + 1 , $column ) );
# right if possible
$counter++ if ( $can-right && is-mine( @input, $row, $column + 1 ) );
# left up
$counter++ if ( $can-left && $can-up && is-mine( @input, $row - 1, $column - 1 ) );
# right up
$counter++ if ( $can-up && $can-right && is-mine( @input, $row - 1, $column + 1 ) );
# left down
$counter++ if ( $can-left && $can-down && is-mine( @input, $row + 1, $column - 1 ) );
# right down
$counter++ if ( $can-down && $can-right && is-mine( @input, $row + 1, $column + 1 ) );
# left up if possible
return $counter;
}
The most complex part is within the compute-mines: in short the function checks if it can move up, down, left and right and diagonal directions without going over the array boundaries. If the move can be done, and in that position there is a mine, the $counter variable is incremented.
It is now turn to use the above functions in the main program:
sub MAIN() {
my @input =
qw/ x * * * x * x x x x /,
qw/ * * * * * * * * * x /,
qw/ * * * * x * x * x * /,
qw/ * * * x x * * * * * /,
qw/ x * * * x * * * * x /;
my $rows = @input.elems;
my $columns = @input[ 0 ].elems;
my ( $current-row, $current-column ) = 0, 0;
for 0 ..^ $rows -> $current-row {
for 0 ..^ $columns -> $current-column {
print is-mine( @input, $current-row, $current-column ) ?? 'x'
!! compute-mines( @input, $current-row, $current-column );
}
print "\n";
}
}
As you can see, the @input array contains the mine field, and the first step is to compute the number of rows and columns, than to do a nested loop to print either the mine or the number computed by compute-mines.
The final result is something like the following:
% raku ch-2.p6
x101x2xxxx
126224355x
0013x3x2x2
111xx41222
x113x2001x
If you have any suggestion then please do share with us perlweeklychallenge@yahoo.com.