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# vim:set ts=4 sw=4 sts=4 et ai wm=0 nu:
#=============================================================================
# LargestRectangleHistogram.pm
#=============================================================================
# Copyright (c) 2020, Bob Lied
#=============================================================================
# Description:
#=============================================================================
package LargestRectangleHistogram;
use strict;
use warnings;
use feature qw(say);
use List::Util qw(max min);
use List::MoreUtils qw(arrayify); # Flattens 2D array into a list
require Exporter;
our @ISA = qw(Exporter);
our @EXPORT = qw();
our @EXPORT_OK = qw();
sub _setup
{
my $self = shift;
for my $row ( 0 .. $self->{_numRow} -1 )
{
for my $col ( 0 .. $self->{_numCol}-1 )
{
$self->{_grid}->[$row][$col] = ( $self->{_list}->[$col] > $row ? '*' : ' ' );
$self->{_area}->[$row][$col] = 0;
}
}
}
sub new
{
my $class = shift;
$class = ref($class) || $class;
my $self = {
_list => [ @_ ],
_numCol => scalar(@_),
_numRow => List::Util::max( @_ ),
_grid => undef,
_area => undef,
_extent => undef,
};
bless $self, $class;
$self->_setup();
return $self;
}
sub _extendLeft
{
my $self = shift;
my ($r, $col) = @_;
my $row = $self->{_grid}->[$r];
$col-- while ( $col >= 0 && $row->[$col] eq '*' );
return $col+1;
}
sub _extendRight
{
my $self = shift;
my ($r, $col) = @_;
my $row = $self->{_grid}->[$r];
$col++ while ( $col < $self->{_numCol} && $row->[$col] eq '*' );
return $col -1;
}
sub _extend
{
my $self = shift;
my ($row, $col) = @_;
my $ext = $self->{_extent};
# Memoize the range if already calculated
return @{$ext->[$row][$col]} if exists $ext->[$row][$col];
my $maxCol = $self->_extendRight($row, $col);
my $minCol = $self->_extendLeft($row, $col);
$ext->[$row][$col] = [ $minCol, $maxCol ] for $minCol .. $maxCol;
return ($minCol, $maxCol);
}
sub _findArea
{
my $self = shift;
my ($row, $col) = @_;
my $grid = $self->{_grid};
my ($minCol, $maxCol) = $self->_extend($row, $col);
my $height = List::Util::min( @{$self->{_list}}[$minCol..$maxCol] );
my $a = $self->{_area}->[$row][$col] = ( ( $maxCol - $minCol + 1) * $height );
# say "[$row][$col] : maxL=$minCol maxR=$maxCol height=$height area=$a";
return $a;
}
sub findLRH
{
my $self = shift;
my $grid = $self->{_grid};
for my $row ( 0 .. $self->{_numRow}-1 )
{
for my $col ( 0 .. $self->{_numCol}-1 )
{
next unless $grid->[$row][$col] eq '*';
my $area = $self->_findArea($row, $col);
}
}
return max(arrayify( @{$self->{_area}} ) );
}
sub _show
{
my $self = shift;
my $g = $self->{_grid};
my $numRow = $self->{_numRow}-1;
my $numCol = $self->{_numCol}-1;
print " ";
for my $c ( 0 .. $numCol )
{
print "[$c]";
}
print "\n";
for my $r ( 0 .. $numRow )
{
print "[$r] ";
say " ", join(' ', @{$g->[$r]}), " ";
}
}
sub display
{
my $self = shift;
my @chart;
for ( my $row = $self->{_numRow}-1 ; $row >= 0 ; $row-- )
{
printf("%2d| ", $row+1);
my $line = join(' ', @{$self->{_grid}->[$row]});
say $line;
}
say ' +', ('-' x ($self->{_numCol}*2));
say ' ', join(' ', @{$self->{_list}});
}
1;
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