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#!/usr/bin/perl
use warnings;
use strict;
use feature 'say';
# Problem: https://perlweeklychallenge.org/blog/perl-weekly-challenge-100/ TASK #2
# Let user select triangle array, 1,2, or 3.
# 0 for random triangle array.
my $number = shift;
$number ||= 0;
do {
print <<EOU;
Usage:
$0 [ 0|1|2 ]
$0 0 # random generate triangle array
$0 1 # use task example 1 triangle
$0 2 # use task example 2 triangle
$0 3 # total is zero triangle array
EOU
exit;
} unless ($number >= 0 and $number <= 3);
# Construct new Triangle Array and init to user selected number
my $t = Triangle_Array->new();
$t->init($number);
# Find the best path using recursion
# The three positional params are: index, path, total
$t->min_path_find( [0,0], [], 0 );
# Explain solution
$t->total();
$t->explain();
$t->solution();
exit;
package Triangle_Array;
sub r {
# return random number between 0 and 9
return int(rand(10));
}
sub new {
my $class = shift;
my $self = {
array => [], # the triangl array
path => [], # best path found
total => 99999, # best total found, init to big magic number
size => 3, # hard coded for triangle with 4 rows, 0 indexed
};
bless $self, $class;
return $self;
}
sub init {
my ($self,$number) = @_;
# task examples
$self->{array} = [ [1], [2,4], [6,4,9], [5,1,7,2] ] if ( $number == 1 );
$self->{array} = [ [3], [3,1], [5,2,3], [4,3,1,3] ] if ( $number == 2 );
# test array, best path is 0 + 0 + 0 + 0 = 0
$self->{array} = [ [0], [1,0], [1,1,0], [1,1,1,0] ] if ( $number == 3 );
# generate randome triangle array
$self->{array} = [
[ r() ],
[ r(),r() ],
[ r(),r(),r() ],
[ r(),r(),r(),r() ],
] if ( $number == 0 );
}
sub total {
my ($self) = @_;
say "Output: " . $self->{total};
}
sub explain {
my ($self) = @_;
say "\nExplanation: The given triangle\n";
# Print triangle, need $x to determine leading pad
my $x = 0;
foreach my $row ( @{$self->{array}} ) {
print " " x ($self->{size} - $x);
foreach my $col ( @{$row} ) {
print " $col ";
}
print "\n";
$x++;
}
}
sub min_path_find {
my ($self, $index, $path, $total) = @_;
# Total along the currect path
# Note: we're making a copy of $path because perl is pass-by-ref.
# Each instance of min_path_find() needs its own path, $this_path.
my $this_path = [ @{$path} ];
push @{$this_path}, $index;
my ($row,$col) = @{$index};
$total += $self->{array}[$row][$col];
# Recurse left and right down the triangle
if ( $row < $self->{size} ) {
$self->min_path_find( [$row+1,$col ], $this_path, $total );
$self->min_path_find( [$row+1,$col+1], $this_path, $total );
}
# Terminal node reached, is this the best path so far?
else {
if ($total < $self->{total}) {
$self->{total} = $total;
$self->{path} = $this_path;
}
}
}
sub solution {
my ($self) = @_;
# Print out solution total
my $out = "The minimum path sum from top to bottom: ";
foreach my $index ( @{$self->{path}} ) {
my ($row,$col) = @{$index};
$out .= $self->{array}[$row][$col] . " + ";
}
$out .= " = $self->{total}";
$out =~ s/ \+ =/ =/;
say "\n$out\n";
# Print out solution path
# Iterate over array refs and print square brackets around
# the element if solution path index [r,c] equals [x,y]
my $x = 0;
foreach my $row ( @{$self->{array}} ) {
my ($r, $c) = @{ $self->{path}[$x] };
print " " x ($self->{size} - $x);
my $y = 0;
foreach my $col ( @{$row} ) {
$out = ($x == $r and $y == $c) ? "[$col]" : " $col ";
print $out;
$y++;
}
$x++;
print "\n";
}
}
1;
__END__
./ch-2.pl 1
Output: 8
Explanation: The given triangle
1
2 4
6 4 9
5 1 7 2
The minimum path sum from top to bottom: 1 + 2 + 4 + 1 = 8
[1]
[2] 4
6 [4] 9
5 [1] 7 2
./ch-2.pl 2
Output: 7
Explanation: The given triangle
3
3 1
5 2 3
4 3 1 3
The minimum path sum from top to bottom: 3 + 1 + 2 + 1 = 7
[3]
3 [1]
5 [2] 3
4 3 [1] 3
./ch-2.pl 3
Output: 0
Explanation: The given triangle
0
1 0
1 1 0
1 1 1 0
The minimum path sum from top to bottom: 0 + 0 + 0 + 0 = 0
[0]
1 [0]
1 1 [0]
1 1 1 [0]
(hist:2226 jobs:0) >>> ./ch-2.pl
Output: 10
Explanation: The given triangle
0
8 7
4 3 7
2 0 0 4
The minimum path sum from top to bottom: 0 + 7 + 3 + 0 = 10
[0]
8 [7]
4 [3] 7
2 [0] 0 4
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