Merge remote-tracking branch 'upstream/master' into ch-075

20 files changed, 1067 insertions, 57 deletions

diff --git a/challenge-075/alexander-pankoff/README b/challenge-075/alexander-pankoff/README
new file mode 100644
index 0000000000..41f67807ac
--- /dev/null
+++ b/challenge-075/alexander-pankoff/README
@@ -0,0 +1 @@
+Solution by Alexander Pankoff
diff --git a/challenge-075/alexander-pankoff/perl/ch-1.pl b/challenge-075/alexander-pankoff/perl/ch-1.pl
new file mode 100755
index 0000000000..ad37e76630
--- /dev/null
+++ b/challenge-075/alexander-pankoff/perl/ch-1.pl
@@ -0,0 +1,86 @@
+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+use feature qw(signatures say);
+no warnings qw(experimental::signatures experimental::smartmatch);
+
+use List::Util qw(any sum0);
+use Scalar::Util qw(looks_like_number);
+
+# You are given an array of positive numbers @A.
+#
+# Write a script to find the larget rectangle histogram created by the given array.
+# BONUS: Try to print the histogram as shown in the example, if possible.
+
+my ( $S, @C ) = @ARGV;
+
+$S //= 6;
+
+@C = ( 1, 2, 4 ) unless @C;
+
+if (   ( any { !looks_like_number( $_ ) } ( $S, @C ) )
+    || ( any { $_ < 1 } @C ) )
+{
+    usage();
+    exit 1;
+}
+
+my @possible_combinations = possible_combinations( \@C, $S );
+
+say scalar @possible_combinations;
+
+exit 0 unless $ENV{DEBUG};
+
+for my $combination ( @possible_combinations ) {
+    say "(" . join( ', ', @$combination ) . ")";
+}
+
+exit 0;
+
+sub possible_combinations ( $coins, $sum, $cur = [] ) {
+    my $current_sum = sum0 @{$cur};
+
+    return $cur   if $current_sum == $sum;
+    die "invalid" if $current_sum > $sum;
+
+    my @solutions;
+    for my $coin ( @$coins ) {
+        eval {
+            my @sub_solutions = possible_combinations( $coins, $sum, [ @$cur, $coin ] );
+            push @solutions, map {
+                [ sort { $a <=> $b } @$_ ]
+            } @sub_solutions;
+        };
+
+        die $@ if $@ and $@ !~ /invalid/;
+    }
+
+    return unique_combinations( @solutions );
+}
+
+sub unique_combinations(@list) {
+    my @out;
+
+    for my $item ( @list ) {
+        my $found = 0;
+        for my $check ( @out ) {
+            if ( @$check ~~ @$item ) {
+                $found = 1;
+                last;
+            }
+        }
+        push @out, $item unless $found;
+    }
+
+    return @out;
+}
+
+sub usage() {
+    say <<END;
+$0 <SUM> [COINS]
+
+  <SUM>   the sum that should be created
+  [COINS] the set of coins available
+END
+}
diff --git a/challenge-075/alexander-pankoff/perl/ch-2.pl b/challenge-075/alexander-pankoff/perl/ch-2.pl
new file mode 100755
index 0000000000..3bd029a638
--- /dev/null
+++ b/challenge-075/alexander-pankoff/perl/ch-2.pl
@@ -0,0 +1,64 @@
+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+use feature qw(signatures say);
+no warnings qw(experimental::signatures);
+
+use Scalar::Util qw(looks_like_number);
+use List::Util qw(any min max);
+
+# You are given an array of positive numbers @A.
+#
+# Write a script to find the larget rectangle histogram created by the given array.
+# BONUS: Try to print the histogram as shown in the example, if possible.
+
+my ( @A ) = @ARGV;
+
+@A = ( 2, 1, 4, 5, 3, 7 ) unless @A;
+
+if ( any { !looks_like_number( $_ ) || $_ < 0 } ( @A ) ) {
+    usage();
+    exit 1;
+}
+
+print_histogram( @A );
+
+say largest_rectangle( @A );
+
+exit 0;
+
+sub largest_rectangle(@cols) {
+    return 0 unless @cols;
+
+    max(
+        rectangle_size( @cols ),
+        largest_rectangle( @cols[ 1 .. $#cols ] ),
+        largest_rectangle( @cols[ 0 .. ( $#cols - 1 ) ] )
+    );
+}
+
+sub rectangle_size(@cols) {
+    return scalar @cols * min @cols;
+}
+
+sub print_histogram(@cols) {
+    my $height = max @cols;
+
+    while ( $height ) {
+        say join( ' ', $height, map { $_ >= $height ? '#' : ' ' } @cols );
+        $height--;
+    }
+
+    say join( ' ', map { '_' } ( 0 .. @cols ) );
+    say join( ' ', ' ', @cols );
+}
+
+sub usage() {
+    say <<END
+$0 [A]
+
+  [A] An array of positive integers
+END
+}
+
diff --git a/challenge-075/dave-jacoby/perl/ch-1.pl b/challenge-075/dave-jacoby/perl/ch-1.pl
new file mode 100755
index 0000000000..670ed4c751
--- /dev/null
+++ b/challenge-075/dave-jacoby/perl/ch-1.pl
@@ -0,0 +1,52 @@
+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+use feature qw{ say signatures state };
+no warnings qw{ experimental };
+
+use List::Util qw{ sum };
+use JSON;
+my $json = JSON->new->pretty->canonical;
+
+my @C      = ( 1, 2, 4 );
+my $S      = 6;
+my @output = resort( coins_sum( [], $S, \@C ) );
+
+make_output( $S, @output );
+
+sub coins_sum ( $input, $sum, $coins ) {
+    my @output;
+    for my $c ( $coins->@* ) {
+        my $input2->@* = $input->@*;
+        push $input2->@*, $c;
+        $input2->@* = sort $input2->@*;
+        my $input3 = join ',', sort $input2->@*;
+        my $sum2 = $sum - $c;
+        if ( $sum2 > 0 ) {
+            push @output, coins_sum( $input2, $sum2, $coins );
+        }
+        elsif ( $sum2 == 0 ) {
+            push @output, $input2;
+        }
+    }
+    return wantarray ? @output : \@output;
+}
+
+sub resort ( @array ) {
+    my $done = {};
+    return grep { !$done->{$_}++ }
+        map { join ',', sort $_->@* } @array;
+}
+
+sub make_output ( $sum, @output ) {
+    my $c = scalar @output;
+    my @letters = 'a'..'z';
+
+    say qq{ There are 6 possible ways to make sum $sum };
+    for my $i ( 0 .. $#output ) {
+        my $l = $letters[$i];
+        say qq{  $letters[$i]) $output[$i] };
+    }
+
+}
diff --git a/challenge-075/dave-jacoby/perl/ch-2.pl b/challenge-075/dave-jacoby/perl/ch-2.pl
new file mode 100755
index 0000000000..68d494a53d
--- /dev/null
+++ b/challenge-075/dave-jacoby/perl/ch-2.pl
@@ -0,0 +1,94 @@
+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+use feature qw{ say signatures state };
+no warnings qw{ experimental };
+
+use List::Util qw{ max };
+use JSON;
+my $json = JSON->new->pretty->canonical;
+
+{
+    my @A = ( 2, 1, 4, 5, 3, 7 );
+    my @histogram = make_histogram(@A);
+    find_largest_rectangle(@histogram);
+}
+{
+    my @A = ( 3, 2, 3, 5, 7, 5 );
+    my @histogram = make_histogram(@A);
+    find_largest_rectangle(@histogram);
+}
+
+exit;
+
+sub make_histogram ( @input ) {
+    my $max = max @input;
+    my @output;
+
+    for my $i ( 0 .. scalar @input ) {
+        my $local = [];
+        my $n     = $input[$i];
+        next unless $n;
+        for my $j ( 1 .. $max ) {
+            push $local->@*, $j <= $n ? '#' : ' ';
+        }
+        push @output, $local;
+    }
+
+    return @output;
+}
+
+sub display_histogram( @histogram ) {
+    my $max_x = scalar @histogram - 1;
+    my $max_y = scalar $histogram[0]->@* - 1;
+    for my $y ( reverse 0 .. $max_y ) {
+        for my $x ( 0 .. $max_x ) {
+            my $c = $histogram[$x][$y];
+            print $c . ' ';
+        }
+        say '';
+    }
+    say '';
+}
+
+sub find_largest_rectangle( @histogram ) {
+    my $max_x = scalar @histogram - 1;
+    my $max_y = scalar $histogram[0]->@* - 1;
+
+    my @output;
+
+    for my $x1 ( 0 .. $max_x - 1 ) {
+        for my $x2 ( $x1 + 1 .. $max_x ) {
+            for my $y1 ( 0 .. $max_y ) {
+                for my $y2 ( $y1 .. $max_y ) {
+
+                    my ( $c1, $c2 ) = ( 0, 0 );
+                    my @v;
+                    for my $x ( $x1 .. $x2 ) {
+                        for my $y ( $y1 .. $y2 ) {
+                            my $v = $histogram[$x][$y];
+                            push @v, $v;
+                            $c1++;
+                            $c2++ if $v eq '#';
+                        }
+                    }
+
+                    next if $c1 != $c2;
+                    push @output, [ $c1, $x1, $y1, $x2, $y2 ];
+                }
+            }
+        }
+    }
+
+    @output = sort { $b->[0] <=> $a->[0] } @output;
+    my ( $c1, $x1, $y1, $x2, $y2 ) = $output[0]->@*;
+    my $columns = join ',', map { $_ + 1 } $x1 .. $x2;
+    my $x       = 1 + $x2 - $x1;
+    my $y       = 1 + $y2 - $y1;
+
+
+    display_histogram(@histogram);
+    say qq{the largest rectangle ($x x $y) is formed by columns ($columns)};
+    say '';
+}
diff --git a/challenge-075/e-choroba/perl/ch-1.pl b/challenge-075/e-choroba/perl/ch-1.pl
new file mode 100755
index 0000000000..9906213aea
--- /dev/null
+++ b/challenge-075/e-choroba/perl/ch-1.pl
@@ -0,0 +1,34 @@
+#! /usr/bin/perl
+use warnings;
+use strict;
+
+# Visible impact for tests #2 and #3.
+use Memoize;
+memoize('_coins_sum');
+
+sub _coins_sum {
+    my ($sum, @coins) = @_;
+    my @r;
+    for my $coin (@coins) {
+        next if $sum < $coin;
+        push @r, $sum == $coin
+                 ? [$coin]
+                 : map [ $coin, @$_ ],
+                   grep $_->[0] >= $coin,
+                   do { no warnings 'recursion';
+                        _coins_sum($sum - $coin, @coins) };
+    }
+    return @r
+}
+
+sub coins_sum {
+    my ($sum, @coins) = @_;
+    my @r = _coins_sum($sum, @coins);
+    return scalar @r
+}
+
+use Test::More tests => 3;
+
+is coins_sum(6,  1, 2, 4), 6;
+is coins_sum(24, 1, 2, 4), 49;
+is coins_sum(80, 2, 7), 6;
diff --git a/challenge-075/e-choroba/perl/ch-2.pl b/challenge-075/e-choroba/perl/ch-2.pl
new file mode 100755
index 0000000000..21e90d6385
--- /dev/null
+++ b/challenge-075/e-choroba/perl/ch-2.pl
@@ -0,0 +1,90 @@
+#! /usr/bin/perl
+use warnings;
+use strict;
+use feature qw{ say };
+use Syntax::Construct qw{ // };
+
+use List::Util qw{ max };
+
+sub draw_histogram {
+    my @columns = @_;
+    my $max = max(@columns);
+    my $max_length = length $max;
+    for my $y (reverse 1 .. $max) {
+        printf "%${max_length}d ", $y;
+        say join ' ', map {
+            sprintf "%${max_length}s", $columns[$_ - 1] >= $y ? '#' : ' '
+        } 1 .. @columns;
+    }
+    say join ' ', ('_' x $max_length) x (1 + @columns);
+    printf "%${max_length}s ", "";
+    say join ' ', map sprintf("%${max_length}d", $_), @columns;
+}
+
+sub _pop {
+    my ($max, $smallest, $columns, $column) = @_;
+    my $s = pop @$smallest;
+    my $area = $columns->[$s] * ($column - ($smallest->[-1] // -1) - 1);
+    $$max = $area if $area > $$max;
+}
+
+sub largest_rectangle {
+    my @columns = @_;
+    my @smallest;
+    my $max = 0;
+    my $column = 0;
+    while ($column <= $#columns) {
+        if (! @smallest || $columns[$column] > $columns[ $smallest[-1] ]) {
+            push @smallest, $column++;
+        } else {
+            _pop(\$max, \@smallest, \@columns, $column);
+        }
+    }
+    _pop(\$max, \@smallest, \@columns, $column) while @smallest;
+    return $max
+}
+
+use Test::More tests => 5;
+
+{
+    open my $stdout, '>', \ my $out;
+    select $stdout;
+    draw_histogram(2, 1, 4, 5, 3, 7);
+    is $out, << '__STDOUT__', 'Print Example 1';
+7           #
+6           #
+5       #   #
+4     # #   #
+3     # # # #
+2 #   # # # #
+1 # # # # # #
+_ _ _ _ _ _ _
+  2 1 4 5 3 7
+__STDOUT__
+}
+
+{
+    open my $stdout, '>', \ my $out;
+    select $stdout;
+    draw_histogram(2, 10);
+    is $out, << '__STDOUT__', 'Longer numbers';
+10     #
+ 9     #
+ 8     #
+ 7     #
+ 6     #
+ 5     #
+ 4     #
+ 3     #
+ 2  #  #
+ 1  #  #
+__ __ __
+    2 10
+__STDOUT__
+}
+
+is largest_rectangle(2, 1, 4, 5, 3, 7), 12, 'Example 1';
+is largest_rectangle(3, 2, 3, 5, 7, 5), 15, 'Example 2';
+
+# https://www.geeksforgeeks.org/largest-rectangle-under-histogram/
+is largest_rectangle(6, 2, 5, 4, 5, 1, 6), 12, 'Sumit Ghosh';
diff --git a/challenge-075/jason-messer/raku/ch-1.p6 b/challenge-075/jason-messer/raku/ch-1.p6
new file mode 100644
index 0000000000..003931441e
--- /dev/null
+++ b/challenge-075/jason-messer/raku/ch-1.p6
@@ -0,0 +1,14 @@
+#! /usr/bin/env rakudo
+
+sub coin-combinations( Int :$sum, :@coins where .all > 0 )  {
+	my @combinations = 1, |(0 xx $sum);
+
+	for @coins -> $coin {
+		loop (my $i = $coin; $i < @combinations.elems; ++$i) {
+			@combinations[$i] += @combinations[$i - $coin];
+		}
+	}
+	return @combinations.tail;
+}
+
+say coin-combinations :sum(6), :coins([1, 2, 4]);
diff --git a/challenge-075/jason-messer/raku/ch-2.p6 b/challenge-075/jason-messer/raku/ch-2.p6
new file mode 100644
index 0000000000..c466853fab
--- /dev/null
+++ b/challenge-075/jason-messer/raku/ch-2.p6
@@ -0,0 +1,38 @@
+#! /usr/bin/env rakudo
+
+sub largest-rectangle( @a ) {
+	my @r = gather loop (my $i = 0; $i < @a.elems; ++$i) {
+
+		my $height = @a[$i];
+		my $width = 1;
+		loop (my $back = $i - 1; $back >= 0; --$back) {
+			last if @a[$back] < $height;
+			$width++;
+		}
+		loop (my $forward = $i + 1; $forward < @a.elems; ++$forward) {
+			last if @a[$forward] < $height;
+			$width++;
+		}
+		take $width *  $height;
+	}
+	return max(@r);
+}
+
+sub print-histogram( @a ) {
+	loop (my $height = max(@a); $height > 0; --$height) {
+		my Str @parts = $height.Str xx 1;
+		@parts.append: @a.map( {$_ >= $height ?? '#' !! ' '} );
+		say @parts.join: ' ';
+	}
+	say "- " x @a.elems + 1;
+	say '  ', @a.join: ' ';
+}
+
+my @A = [2, 1, 4, 5, 3, 7];
+my @B = [3, 2, 3, 5, 7, 5];
+
+print-histogram(@A);
+say "area: ", largest-rectangle(@A);
+
+print-histogram(@B);
+say "area: ", largest-rectangle(@B);
diff --git a/challenge-075/jo-37/perl/ch-1.pl b/challenge-075/jo-37/perl/ch-1.pl
new file mode 100755
index 0000000000..2c75a7fc10
--- /dev/null
+++ b/challenge-075/jo-37/perl/ch-1.pl
@@ -0,0 +1,39 @@
+#!/usr/bin/perl
+
+use Test2::V0;
+use List::Util qw(any min);
+
+# Assemble given sum (1st arg) from a set of coins having values as
+# specified in the remaining arguments.
+sub assemble;
+sub assemble {
+	my ($sum, @coins) = @_;
+
+	# There is no solution if the sum is less than the smallest coin.
+	return if $sum < min @coins;
+
+	# If a coin matches the given sum, this gives one (non-recursive)
+	# assembly.
+	((any {$sum == $_} @coins) ? [$sum] : (),
+	# Try each coin for further assemblies.	
+	map {
+		my $coin = $_;
+		# Reduce the sum by the selected coin and combine that one with
+		# all possible assemblies of the reduced sum using solely coins
+		# that are not smaller than the selected.
+		map [$coin, @$_], assemble $sum - $coin, grep $_ >= $coin, @coins;
+	} @coins);
+}
+
+is [assemble 6, 1, 2, 4],
+	bag {
+		item([1, 1, 1, 1, 1, 1]),
+		item([1, 1, 1, 1, 2]),
+		item([1, 1, 2, 2]),
+		item([1, 1, 4]),
+		item([2, 2, 2]),
+		item([2, 4]),
+		end()
+	}, 'example from challenge';
+
+done_testing;
diff --git a/challenge-075/jo-37/perl/ch-2.pl b/challenge-075/jo-37/perl/ch-2.pl
new file mode 100755
index 0000000000..251539c6ae
--- /dev/null
+++ b/challenge-075/jo-37/perl/ch-2.pl
@@ -0,0 +1,124 @@
+#!/usr/bin/perl
+
+
+# A tailor-made class for this task.
+package Rectangle;
+
+use strict;
+use warnings;
+use List::Util qw(min);
+use overload
+	'<=>' => \&cmp_rect,	# compare by size
+	'.=' => \&position,		# set position
+	'""' => \&show;			# stringify
+
+# Create a new rectangle over the full length of
+# the given (partial) histogram and with maximum height.
+sub new {
+	my $class = shift;
+
+	bless {height => min(@_) // 0,
+		length => scalar @_,
+		position => -1}, $class;
+}
+
+# Compare two rectangles by size.
+sub cmp_rect {
+	my ($self, $other) = @_;
+
+	$self->{length} * $self->{height} <=> $other->{length} * $other->{height};
+}
+
+# Set (end) position.
+sub position {
+	my ($self, $pos) = @_;
+
+	$self->{position} = $pos;
+	$self;
+}
+
+# String representation.
+sub show {
+	my $self = shift;
+
+	sprintf "size=%d, length=%d, position=%d, height=%d",
+		$self->{length} * $self->{height}, $self->{length},
+		$self->{position}, $self->{height};
+}
+
+# Check if point is contained in rectangle.
+sub contains {
+	my ($self, $ix, $height) = @_;
+
+	$ix >= $self->{position} - $self->{length} + 1 &&
+		$ix <= $self->{position} && $height <= $self->{height};
+}
+
+package main;
+
+use strict;
+use warnings;
+use List::Util qw(max reduce);
+
+# Find the largest rectangle inside a histogram.
+# The Rectangle constructor, comparator and assignment operator
+# are specifically designed to offer a terse implementation here.
+sub max_rect {
+
+	# Slide over all elements seeking for the maximum rectangle
+	reduce {
+		my $pos = $b;
+		# Slide over all windows ending at the selected position.
+		reduce {
+			# Get the maximum rectangle over the full window length.
+			my $rect = Rectangle->new(@_[$b .. $pos]);
+			# If the new rectangle is larger than the current maximum,
+			# set the position and use it as the new maximum.
+			$rect > $a ? $rect .= $pos : $a;
+		} $a, 0 .. $b;
+	} Rectangle->new, 0 .. $#_;
+}
+
+# Create the histogram row data at the given height:
+# - empty, if height is above the value
+# - asterisk, if the point is inside the maximum rectangle
+# - hash otherwise.
+sub hist_chars {
+	my ($max, $height) = (shift, shift);
+
+	map $_[$_] >= $height ?
+		$max->contains($_, $height) ?
+		'*' : '#' : '', 0 .. $#_;
+}
+
+# Generate a format string. Produces $size + 1 items of equal
+# length $len that are separated by one blank. The first item has
+# conversion $first, the rest have conversion $rest.
+sub gen_fmt ($$$$) {
+	my ($len, $first, $rest, $size) = @_;
+
+	"%${len}${first}" . " %${len}${rest}" x $size . "\n";
+}
+
+# Print the histogram.
+sub print_hist {
+	my $max = shift;
+
+	my $height = max @_;
+	my $len = length $height;
+
+	my $fmt = gen_fmt $len, 'd', 's', @_;
+	do {
+		printf $fmt, $height, hist_chars $max, $height, @_
+	} while --$height;
+	printf gen_fmt($len, 's', 's', @_), ('-') x (@_ + 1);
+	printf gen_fmt($len, 's', 'd', @_), '', @_;
+}
+
+# main
+
+for my $hist ([2, 1, 4, 5, 3, 7], [3, 2, 3, 5, 7, 5, 2]) {
+	my $max = max_rect @$hist;
+	print_hist $max, @$hist;
+	print "max rectangle: $max\n\n";
+}
diff --git a/challenge-075/lubos-kolouch/perl/ch-1.pl b/challenge-075/lubos-kolouch/perl/ch-1.pl
new file mode 100644
index 0000000000..756cba3ebf
--- /dev/null
+++ b/challenge-075/lubos-kolouch/perl/ch-1.pl
@@ -0,0 +1,27 @@
+#!/usr/bin/env perl
+use strict;
+use warnings;
+# Perl weekly challenge 075 Task 1 - Coins sum
+
+
+sub count {
+
+    my ($coins, $target_sum) = @_;
+
+    my @ways = (0) x $target_sum;
+    $ways[0] = 1;
+
+    for my $coin_pos (0..scalar @$coins - 1) {
+        for my $j (0..$target_sum) {
+            $ways[$j] += $ways[$j - $coins->[$coin_pos]] if $coins->[$coin_pos] <= $j;
+        }
+    }
+
+    return $ways[$target_sum];
+}
+
+use Test::More;
+
+is(count([1, 2, 4], 6), 6, 'Test case 1, 2, 4 and 6');
+is(count([1, 5, 10], 12), 4, 'Test case 1, 5, 10 and 12');
+done_testing;
diff --git a/challenge-075/lubos-kolouch/python/ch-1.py b/challenge-075/lubos-kolouch/python/ch-1.py
new file mode 100644
index 0000000000..c706f7f5a0
--- /dev/null
+++ b/challenge-075/lubos-kolouch/python/ch-1.py
@@ -0,0 +1,21 @@
+#!/usr/bin/env python
+""" Perl weekly challenge 075 Task 1 - Coins sum """
+
+
+def count(coins, target_sum):
+    """ count the ways we can sum coins """
+
+    ways = [0] * (target_sum + 1)
+
+    ways[0] = 1
+
+    for value in coins:
+        for j, _ in enumerate(ways):
+            if value <= j:
+                ways[j] += ways[j - value]
+
+    return ways[target_sum]
+
+
+assert count([1, 2, 4], 6) == 6
+assert count([1, 5, 10], 12) == 4
diff --git a/challenge-075/mohammad-anwar/blog1.txt b/challenge-075/mohammad-anwar/blog1.txt
new file mode 100644
index 0000000000..24c9c488d7
--- /dev/null
+++ b/challenge-075/mohammad-anwar/blog1.txt
@@ -0,0 +1 @@
+https://www.youtube.com/watch?v=DQr7xHJYZ5I
diff --git a/challenge-075/mohammad-anwar/perl/ch-2.pl b/challenge-075/mohammad-anwar/perl/ch-2.pl
index 7749fa9364..8e962979ad 100755
--- a/challenge-075/mohammad-anwar/perl/ch-2.pl
+++ b/challenge-075/mohammad-anwar/perl/ch-2.pl
@@ -3,62 +3,107 @@
 #
 # Perl Weekly Challenge - 075
 #
-# Task #1: Coins Sum
+# Task #2: Largest Rectangle Histogram
 #
 # https://perlweeklychallenge.org/blog/perl-weekly-challenge-075
 #
 
 use strict;
 use warnings;
+use List::Util qw(min max);
 
-my $COINS = $ARGV[0] || "1, 2, 4";
-my $SUM   = $ARGV[1] || 6;
+my $L = $ARGV[0] || "2, 1, 4, 5, 3, 7";
 
-print "Possible ways to achieve the target: ",
-      coins_sum(prepare($COINS), $SUM), "\n";
+my $list = prepare($L);
+print chart($list), "\n\n";
+print "Largest Rectangle Histogram: ", largest_rectangle_histogram($list), "\n";
 
 #
 #
 # METHODS
 
-sub coins_sum {
-    my ($coins, $sum) = @_;
+sub largest_rectangle_histogram {
+    my ($list) = @_;
 
-    my $size = $#$coins;
-    return 0 if ($size == -1 || $sum <= 0);
+    my $i   = 0;
+    my $max = 0;
+    foreach my $n (@$list) {
 
-    my $matrix;
+        my ($left, $right) = (0, 0);
+        $left  = go_left($i, $list)  if ($i > 0);
+        $right = go_right($i, $list) if ($i <= $#$list);
 
-    # Sum of 0 can be achieved in one possible way.
-    $matrix->[$_][0] = 1 for (0 .. $size+1);
+        my @heights = (@$list)[$i - $left .. $i + $right];
+        my $size    = min(@heights) * @heights;
+        $max = $size if ($size > $max);
 
-    foreach my $i (0 .. $size) {
+        $i++;
+    }
 
-        foreach my $j (1 .. $sum) {
+    return $max;
+}
 
-            my $include_current = 0;
-            my $exclude_current = 0;
+sub go_left {
+    my ($i, $list) = @_;
 
-            if ($coins->[$i] <= $j) {
-                $include_current = $matrix->[$i][$j - $coins->[$i]];
-            }
+    my $c = $list->[$i];
+    my $j = 0;
+    while ($i > 0) {
+        $i--;
+        last if ($list->[$i] < $c);
+        $j++;
+    }
 
-            if ($i > 0) {
-                $exclude_current = $matrix->[$i - 1][$j];
-            }
+    return $j;
+}
+
+sub go_right {
+    my ($i, $list) = @_;
 
-            $matrix->[$i][$j] = $include_current + $exclude_current;
+    my $c = $list->[$i];
+    my $j = 0;
+    while ($i < $#$list) {
+        $i++;
+        last if ($list->[$i] < $c);
+        $j++;
+    }
+
+    return $j;
+}
+
+sub chart {
+    my ($list) = @_;
+
+    my $max   = max(@$list);
+    my $chart = [];
+    my $row   = 1;
+    foreach (1..$max) {
+        my $data = "";
+        foreach my $i (0..$#$list) {
+            if ($row <= $list->[$i]) {
+                $data .= " #";
+            }
+            else {
+                $data .= "  ";
+            }
         }
+        $row++;
+        push @$chart, sprintf("%d%s", $_, $data);
     }
 
-    return $matrix->[$size][$sum];
+    my ($histogram, $line, $size) = ("", "", "  ");
+    $histogram = join "\n", (reverse @$chart);
+    $line .= "_ " for (0..$#$list + 1);
+    $size .= join " ", @$list;
+
+    return join "\n", $histogram, $line, $size;
 }
 
 sub prepare {
-    my ($coins) = @_;
+    my ($list) = @_;
 
-    if (defined $coins) {
-        $coins =~ s/\s//g;
-        return [ split /\,/, $coins ];
+    if (defined $list) {
+        $list =~ s/\s//g;
+        return [ split /\,/, $list ];
     }
 }
diff --git a/challenge-075/mohammad-anwar/perl/ch-2.t b/challenge-075/mohammad-anwar/perl/ch-2.t
index c2d32443b5..51ba0dec90 100755
--- a/challenge-075/mohammad-anwar/perl/ch-2.t
+++ b/challenge-075/mohammad-anwar/perl/ch-2.t
@@ -3,7 +3,7 @@
 #
 # Perl Weekly Challenge - 075
 #
-# Task #1: Coins Sum
+# Task #2: Largest Rectangle Histogram
 #
 # https://perlweeklychallenge.org/blog/perl-weekly-challenge-075
 #
@@ -11,12 +11,10 @@
 use strict;
 use warnings;
 use Test::More;
+use List::Util qw(min max);
 
-is coins_sum(prepare("1, 2"),        5), 3;
-is coins_sum(prepare("1, 2, 3"),     5), 5;
-is coins_sum(prepare("1, 2, 4"),     6), 6;
-is coins_sum(prepare("25, 10, 5"),  30), 5;
-is coins_sum(prepare("9, 6, 5, 1"), 11), 6;
+is(largest_rectangle_histogram(prepare("2, 1, 4, 5, 3, 7")), 12, "example 1");
+is(largest_rectangle_histogram(prepare("3, 2, 3, 5, 7, 5")), 15, "example 2");
 
 done_testing;
 
@@ -24,44 +22,88 @@ done_testing;
 #
 # METHODS
 
-sub coins_sum {
-    my ($coins, $sum) = @_;
+sub largest_rectangle_histogram {
+    my ($list) = @_;
 
-    my $size = $#$coins;
-    return 0 if ($size == -1 || $sum <= 0);
+    my $i   = 0;
+    my $max = 0;
+    foreach my $n (@$list) {
 
-    my $matrix;
+        my ($left, $right) = (0, 0);
+        $left  = go_left($i, $list)  if ($i > 0);
+        $right = go_right($i, $list) if ($i <= $#$list);
 
-    # Sum of 0 can be achieved in one possible way.
-    $matrix->[$_][0] = 1 for (0 .. $size+1);
+        my @heights = (@$list)[$i - $left .. $i + $right];
+        my $size    = min(@heights) * @heights;
+        $max = $size if ($size > $max);
 
-    foreach my $i (0 .. $size) {
+        $i++;
+    }
 
-        foreach my $j (1 .. $sum) {
+    return $max;
+}
 
-            my $include_current = 0;
-            my $exclude_current = 0;
+sub go_left {
+    my ($i, $list) = @_;
 
-            if ($coins->[$i] <= $j) {
-                $include_current = $matrix->[$i][$j - $coins->[$i]];
-            }
+    my $c = $list->[$i];
+    my $j = 0;
+    while ($i > 0) {
+        $i--;
+        last if ($list->[$i] < $c);
+        $j++;
+    }
 
-            if ($i > 0) {
-                $exclude_current = $matrix->[$i - 1][$j];
-            }
+    return $j;
+}
+
+sub go_right {
+    my ($i, $list) = @_;
 
-            $matrix->[$i][$j] = $include