Perl Weekly Challenge 73: reduction to min

One way to let me improve my knowledge about Raku (aka Perl 6) is to implement programs in it. Unluckily, I don’t have any production code to implement in Raku yet (sob!). So, why not try solving the Perl Weekly Challenge tasks?

In the following, the assigned tasks for Challenge 73.

Sunday Rush

I was on vacation this week, so I had to complete this PWC on sunday as I got home. The fun part is that tomorrow another PWC will hit my inbox.
Luckily, this PWC was not too difficult to me.

PWC 73 - Task 1

The first task was related to find out the minimum in an array window. Since Raku allows for array slices, and the [min] reduction operator does the trick, the only difficult in this task was to correctly compute the size of the window to work on:

sub MAIN( Int $S where { 0 < $S },
          *@A where { @A.elems > $S } ) {

    my @mins;
    for 0 .. ( @A.elems - $S ) {
        @mins.push: [min] @A[ $_ ..^ ( $_ + $S ) ];

    @mins.join( ',' ).say;

I decided to put $S as first positional to allow a slurpy parameter to consume all remaining numbers.
After that I iterated over the windows, computing the minimum value and assigning it to the @mins array.

PWC 73 - Task 2

The second task required to find out the minimum element on the left side of an array element of integers. Again, the [min] reduction operator was the best candidate to me, with the only exception that in case there was not a value less than the current one the special value of zero has to be used.

sub MAIN( *@A where { @A.grep( * ~~ Int ).elems == @A.elems } ) {
    my @mins;
    for 0 ..^ @A.elems {
        my $current-min = $_ == 0 ?? 0 !! [min] @A[ 0 ..^ $_ ];
        @mins.push: $current-min < @A[ $_ ] ?? $current-min !! 0;

    @mins.join( ',' ).say;

Since slurpy arrays cannot be typed, I had to ensure that every element of the array was an integer.
The first element of the array cannot have nothing on its left, so it defaults to zero. The other elements assume the [min] of the slice from the first element to the current one. If such value, stored into $current-min is less than the current element @A[$_] then it is pushed to the array of @mins, otherwise zero is pused.

The article Perl Weekly Challenge 73: reduction to min has been posted by Luca Ferrari on August 16, 2020