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#!/usr/bin/env perl

...
my %seen; 
$seen{join $; => @{$hash{$_}}}++ and delete $hash{$_} for keys %hash;
dd \%hash;

{ a => [1, 2], b => [2, 3], c => [1, 2] }
{ a => [1, 2], b => [2, 3] }