# Some example data...
my @curr = (
	{
		node => 'Alice',
		link => 'A to B',
		load => 20,
	},
	{
		node => 'Alice',
		link => 'A to C',
		load => 24,
	},
	{
		node => 'Bob',
		link => 'B to C',
		load => 12,
	},
	{
		node => 'Bob',
		link => 'B to A',
		load => 3,
	},
	{
		node => 'Carol',
		link => 'C to A',
		load => 14,
	},
	{
		node => 'Carol',
		link => 'C to B',
		load => 7,
	},
);

my @prev = (
	{
		node => 'Alice',
		link => 'A to B',
		load => 20,
	},
	{
		node => 'Alice',
		link => 'A to C',
		load => 24,
	},
	{
		node => 'Bob',
		link => 'B to C',
		load => 15,
	},
	{
		node => 'Bob',
		link => 'B to A',
		load => 3,
	},
	{
		node => 'Carol',
		link => 'C to A',
		load => 12,
	},
	{
		node => 'Carol',
		link => 'C to B',
		load => 3,
	},
);


# Transform to a hash. This happens in roughly O(n) time.
my %hash;
$hash{"$_->{node}|$_->{link}"}            = +{%$_}     for @curr;
$hash{"$_->{node}|$_->{link}"}{prev_load} = $_->{load} for @prev;

# Again, looping through the hash values is roughly O(n).
for (values %hash)
{
	printf
		"Node '%s', link '%s': previously %d, currently %d.\n",
		$_->{node},
		$_->{link},
		$_->{prev_load},
		$_->{load},
		unless $_->{load} == $_->{prev_load};
}