#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

#protos
sub mergeSort( \@ );

my @unsortedData = ( 5, 4, 7, 2, 1, 3, 6, 9, 8, 10 );

# show the original data to screen
for( @unsortedData ) {
	print "$_  ";
}
print "\n";

my $sortedData = &mergeSort( \@unsortedData );

# show the new data to screen
for( @$sortedData ) {
	print "$_  ";
}
print "\n";

### dereferencing of arrays isnt working in below method

sub mergeSort( \@arrayRef ) {
	my ( $data ) = @_;

	if( @$data < 2 ) { return $data; }  # if there is less then two items it's already sorted!!
	
	use integer;
	#split the array into two parts
	my $middle = @$data / 2; 
	print "middle: $middle\n";
	
	my @leftSide = (); 
	print "LeftSide:\n";
	for( my $i = 0; $i < $middle; $i++ ) {
		@leftSide[$i] = @$data[$i];
		print "@leftSide[$i] ";
	}
	print "\n";
	my @rightSide = (); 
	print "RightSide:\n";
	for( my $i = $middle; $i < @$data; $i++ ) {
		@rightSide[$i - $middle] = @$data[$i];
		print "@rightSide[$i - $middle] ";
	}
	print "\n";
	&mergeSort( @leftSide );
	&mergeSort( @rightSide );
	&merge( @leftSide, @rightSide, $data );
	return $data;
}

sub merge {
	my ( @groupA, @groupB, $dataRef ) = @_;
	my $i = 0; my $j = 0; my $k = 0;
	
	while( $i < @groupA && $j < @groupB ) {
		if( @groupA[$i] <= @groupB[$j] ) {
			@$dataRef[$k] = @groupA[$i];
			$i++;
		}
		else {
			@$dataRef[$k] = @groupB[$j];
			$j++;
		}
		$k++;
	}
	while( $i < @groupA ) {
		@$dataRef[$k] = @groupA[$i];
		$i++;
		$k++;
	}
	while( $j < @groupB ) {
		@$dataRef[$k] = @groupB[$j];
		$j++;
		$k++;
	}
}

##</code><code>##

5  4  7  2  1  3  6  9  8  10  
middle: 5
LeftSide:
5 4 7 2 1 
RightSide:
3 6 9 8 10 
Can't use string ("5") as an ARRAY ref while "strict refs" in use at mergeSort.pl line 34.