my %map;
push @{$map{K1}}, 'V1';
push @{$map{K1}}, 'V2';
push @{$map{K2}}, 'V3';
push @{$map{K3}}, 'V4';
print Dumper(\%map);

# or

my %map2;
$map2{K1} = ['V1', 'V2'];
$map2{K2} = ['V3'];
$map2{K3} = ['V4'];
print Dumper(\%map2);

# or

my %map3;
@map3{'K1','K2','K3'} = (['V1', 'V2'], ['V3'], ['V4']);
print Dumper(\%map3);

# etc.