## BLOG: The Weekly Challenge #079

Sunday, Sep 27, 2020| Tags: Perl, Raku ### 4. TASK #2: Trapped Rain Water

I really enjoyed this week task. I had lots of fun working with the `Trapped Rain Water` task.

This week, I was too busy with my `\$work`, so couldn’t do either `Swift` coding or live video session. However I promise, I will catch up next week.

Sorry, I couldn’t make video for this week tasks.

However, you can take a look at my past week videos by visiting my YouTube Channel.

Last but not the least, I would to love hear your views/opinions with regard to anything I do.

Let me share my solutions to the The Weekly Challenge - 079.

## TASK #1 › Count Set Bits

#### Submitted by Mohammad S Anwar

You are given a positive number `\$N`.

Write a script to count the total numbrer of set bits of the binary representations of all numbers from `1` to `\$N` and return `\$total_count_set_bit % 1000000007`.

Because of the simplicity of the task, I tried to make it as short as possible. Code is self explanatory.

``````sub count_set_bits {
my \$c = 0;
\$c   += (sprintf "%b", \$_) =~ tr/1/1/ for 1..shift;
return \$c % 1000000007;
}
``````

For Raku solution, I had to consult the document to remind myself how to get binary of given decimal. Apart from that, nothing special about this solution.

Having said that it still look elegant, at least to me.

``````sub count-set-bits(Int \$n) {
my \$c = 0;
(1..\$n).map( -> \$i { \$c += [+] \$i.base(2).comb; });
return \$c % 1000000007;
}
``````

Time to stitch together everything and solve the task.

``````use strict;
use warnings;

my \$N = \$ARGV || 4;
die "ERROR: Invalid number [\$N].\n" unless (\$N =~ /^\d+\$/);
print count_set_bits(\$N), "\n";
``````

and here goes Raku solution.

``````use v6.d;

sub MAIN(Int :\$N = 4) { count-set-bits(\$N).say }
``````

with some standard unit testing to make keep happy the developer inside me.

``````use strict;
use warnings;
use Test::More;

is(count_set_bits(4), 5, "testing example 1");
is(count_set_bits(3), 4, "testing example 2");

done_testing;
``````

along with Raku unit test as well.

``````use Test;

is count-set-bits(4), 5, "testing example 1";
is count-set-bits(3), 4, "testing example 2";

done-testing;
``````

## TASK #2 › Trapped Rain Water

#### Submitted by Mohammad S Anwar

You are given an array of positive numbers `@N`.

Write a script to represent it as Histogram Chart and find out how much water it can trap.

Fun task of the week, I really enjoyed playing with algorithm that came to my mind first.

``````sub trapped_rain_water {
my (\$arrayref) = @_;

my @a   = ();
my \$p   = 0;
my \$trw = 0;
foreach my \$n (@\$arrayref) {
if (\$p == 0 || \$p >= \$n) {
\$p = \$n if (@a == 0 || (\$p == 0 && \$n > \$p));
push @a, \$n;
}
else {
push @a, \$n;
\$trw += fetch_trapped_water(@a);
@a = (\$n);
\$p = \$n if (\$p < \$n);
}
}

# are there any left over to be processed?
if (@a > 1) {
\$trw += fetch_trapped_water(@a);
}

return \$trw;
}
``````

The real work done in the following `sub fetch_trapped_water()`.

``````sub fetch_trapped_water {
my (@array) = @_;

# remove any smaller tower from the start
do {
if (\$array == 0) {
shift @array;
}
} until (\$array > 0);

# remove any smaller tower from the end
do {
if (\$array[-1] < \$array[-2]) {
pop @array;
}
}
until (\$array[-1] > \$array[-2]);

my \$max = min(\$array, \$array[-1]) * (@array - 2);
\$max -= \$array[\$_] for 1..@array-2;

return \$max;
}
``````

I nicked the following `sub histogram()` from my earlier week solution. Didn’t want to go through the pain again.

``````sub histogram {
my (\$arrayref) = @_;

my \$max   = max(@\$arrayref);
my \$chart = [];
my \$row   = 1;
foreach (1..\$max) {
my \$data = "";
foreach my \$i (0..\$#\$arrayref) {
if (\$row <= \$arrayref->[\$i]) {
\$data .= " #";
}
else {
\$data .= "  ";
}
}
\$row++;
push @\$chart, sprintf("%d%s", \$_, \$data);
}

my (\$histogram, \$line, \$size) = ("", "", "  ");
\$histogram = join "\n", (reverse @\$chart);
\$line .= "_ " for (0..\$#\$arrayref + 1);
\$size .= join " ", @\$arrayref;

return join "\n", \$histogram, \$line, \$size;
}
``````

Helper `sub to_arrayref()` to convert the command line string to array ref.

``````sub to_arrayref {
my (\$l) = @_;

die "ERROR: Missing list.\n"      unless defined \$l;
die "ERROR: Invalid list [\$l].\n" unless (\$l =~ /^[\-?\d\,?\s?]+\$/);

\$l =~ s/\s//g;
return [ split /\,/, \$l ];
}
``````

Literal translation of Perl solution.

``````sub trapped-rain-water(*@array where .all ~~ PositiveInt) {

my @a   = ();
my \$p   = 0;
my \$trw = 0;
for @array -> \$n {
if \$p == 0 || \$p >= \$n {
\$p = \$n if @a == 0 || (\$p == 0 && \$n > \$p);
@a.push: \$n;
}
else {
@a.push: \$n;
\$trw += fetch-trapped-water(@a);
@a = \$n;
\$p = \$n if \$p < \$n;
}
}

# are there any left over to be processed?
if @a.elems > 1 {
\$trw += fetch-trapped-water(@a);
}

return \$trw;
}
``````
``````sub fetch-trapped-water(*@array where .all ~~ PositiveInt) {

# remove any smaller tower from the start
repeat {
if @array == 0 {
@array.shift;
}
} until @array > 0;

# remove any smaller tower from the end
repeat {
if @array[*-1] < @array[*-2] {
@array.pop;
}
}
until @array[*-1] > @array[*-2];

my \$max = (@array, @array[*-1]).min * (@array.elems - 2);
\$max -= @array[\$_] for 1..@array.elems - 2;

return \$max;
}
``````

Here also I borrowed this `sub chart()` from my past week solutions.

``````sub chart(*@list where @list.elems > 1 && all(@list) ~~ PositiveInt --> Str) {

my \$max   = @list.max;
my \$chart = [];
my \$row   = 1;
for 1 .. \$max -> \$n {
my Str \$data = "";
for 0 .. @list.elems-1 -> \$i {
if \$row <= @list[\$i] {
\$data ~= " #";
}
else {
\$data ~= "  ";
}
}

\$row += 1;

\$chart.push: sprintf("%d%s", \$n, \$data);
}

my (Str \$histogram, Str \$line, Str \$size) = ("", "", "  ");
\$histogram = \$chart.reverse.join("\n");
\$line ~= "_ " for 0 .. @list.elems;
\$size ~= @list.join(" ");

return (\$histogram, \$line, \$size).join("\n");
}
``````

Time to solve the task in Perl.

``````use strict;
use warnings;
use List::Util qw(min max);

my \$L = \$ARGV || "2, 1, 4, 1, 2, 5";
printf("%s\n\n", histogram(to_arrayref(\$L)));
printf("Trapped Rain Water: %d\n", trapped_rain_water(to_arrayref(\$L)));
``````

Followed by Raku.

``````use v6.d;

subset PositiveInt of Int where * >= 0;

sub MAIN(*@N where @N.elems > 1 && all(@N) ~~ PositiveInt) {
chart(@N).say;
trapped-rain-water(@N).say;
}
``````

Good set of test cases to make it complete.

``````use strict;
use warnings;
use Test::More;
use List::Util qw(min);

is( trapped_rain_water([0, 1, 2, 3, 4, 5]),
0, "testing [0, 1, 2, 3, 4, 5]");

is( trapped_rain_water([2, 1, 4, 1, 2, 5]),
6, "testing [2, 1, 4, 1, 2, 5]");

is( trapped_rain_water([3, 1, 3, 1, 1, 5]),
6, "testing [3, 1, 3, 1, 1, 5]");

is( trapped_rain_water([0, 1, 0, 2, 1, 0, 1, 3, 2, 1, 2, 1]),
6, "testing [0, 1, 0, 2, 1, 0, 1, 3, 2, 1, 2, 1]");

done_testing;
``````

Unit testing in Raku as well.

``````use Test;

subset PositiveInt of Int where * >= 0;

is trapped-rain-water(0, 1, 2, 3, 4, 5),
0, "testing: 0, 1, 2, 3, 4, 5";
is trapped-rain-water(3, 1, 3, 1, 1, 5),
6, "testing: 3, 1, 3, 1, 1, 5";
is trapped-rain-water(2, 1, 4, 1, 2, 5),
6, "testing: 2, 1, 4, 1, 2, 5";
is trapped-rain-water(0, 1, 0, 2, 1, 0, 1, 3, 2, 1, 2, 1),
6, "testing: 0, 1, 0, 2, 1, 0, 1, 3, 2, 1, 2, 1";

done-testing;
``````

That’s it for this week. Speak to you soon.

## SO WHAT DO YOU THINK ?

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