use strict;
use warnings;
use Data::Dumper;

my (%required_sources, %remaining_keys);
my $count = 0;
my ($previous_key, $previous_source) = ("", "");

my @DATA = qw /
0000002D9D62AEBE1E0E9DB6C4C4C7C16A163D2C|2f214516cdcab089e83f3e5094928fe9611f2f51
000000A9E47BD385A0A3685AA12C2DB6FD727A20|2adeac692d450c54f8830014ee6cbe3a958c1e60
00000142988AFA836117B1B572FAE4713F200567|04bb7bbed62376f9aaec15fe6f18b89b27a4c3d8
00000142988AFA836117B1B572FAE4713F200567|6935a8fc967a6ffc20be0f07f2bb4a46072a397e
00000142988AFA836117B1B572FAE4713F200567|8c88f4f3c4b1aff760a026759ae807af6c40e015
00000142988AFA836117B1B572FAE4713F200567|974c820f53aded6d6e57ca8de2c33206e2b5f439
00000142988AFA836117B1B572FAE4713F200567|b05be3e17bb9987ffb368696ee916dd9b9c2f9b3
000001BCBC3B7C8C6E5FC59B686D3568132D218C|0d4c09539f42165bb8b1ab890fe6dc3d3ca838b3
000001BCBC3B7C8C6E5FC59B686D3568132D218C|9fd421d4e020788100c289d21e4b9297acaaff62
000001BCBC3B7C8C6E5FC59B686D3568132D218C|d09565280ebae0a37ca9385bc39c0a777a446554
000001E4975FA18878DF5C0989024327FBE1F4DF|55b8ece03f4935f9be667e332d52f7db3e17b809
000001EF1880189B7DE7C15E971105EB6707DE83|cd15550344b5b9c2785a13ef9583015f267ad667
000002F2D7CB4D4B548ADC623F559683D6F59258|36bed8bdb6d66fb67f409166f5db64b02199812f
0000034C9033333F8F58D9C7A64800F509962F3A|3c4b0a3c1acf6e03111805a0d8b4e879df112b7a
000003682106A4CB4F9D3B1B6E5C08820FCFD1B2|cd15550344b5b9c2785a13ef9583015f267ad667
00000368B9CFE1B4CF9F3D38F3EFD82840BA280D|50edd315b9217345b1728c38b02657df42043197
000003A16A5A1C6CCDDBE548E85261422489A458|691845459c0ad35b28cce4dffc0e3ee8912fb0f5
0000046FD530A338D03422C7D0D16A9EE087ECD9|13e213f346ce624e9be99b356ab9125af563a375
0000046FD530A338D03422C7D0D16A9EE087ECD9|67c0da2da88a23a803733cea951e84974b34d029
00000472E2B96A6CD0CBE8614779C5C8197BB42D|0c5e6cdb06c52160ded398d17392246269165e0a
/;


for (@DATA) {
	my ($key, $source) = split /\|/, $_;
	if ($key eq $previous_key) {
		$count ++;
	} else {
		$required_sources{$previous_source} = 1 if $count == 1;
		$previous_key = $key;
		$count = 1;
	}
	$previous_source = $source;
}
$required_sources{$previous_source} = 1 if $count == 1;

for (@DATA) {
	my ($key, $source) = split /\|/, $_;
	$remaining_keys{$key} = $source unless exists $required_sources{$source};
}

print "Remaining keys (before the while loop): \n", Dumper \%remaining_keys;

my $continue = 1;
while ($continue and keys %remaining_keys) {
	my %unique_keys;
	$unique_keys{$_}++ for keys %remaining_keys;
	$continue = 0;
	for my $key (keys %unique_keys) {
		if ($unique_keys{$key} == 1) {
			my $source = $remaining_keys{$key};
			$required_sources{$source} = 1;
			delete $remaining_keys{$key};
			my @additional_keys_to_be_deleted = grep {$remaining_keys{$_} eq $source} keys %remaining_keys;
			delete $remaining_keys{$_} for @additional_keys_to_be_deleted ;
			$continue = 1;
		}
	}
}	


print "Required sources : \n", Dumper \%required_sources;
print "\n\n";
print "Remaining keys: \n", Dumper \%remaining_keys;

##</code><code>##

$ perl  key_source.pl
Remaining keys (before the while loop):
$VAR1 = {
          '0000046FD530A338D03422C7D0D16A9EE087ECD9' => '67c0da2da88a23a803733cea951e84974b34d029',
          '00000142988AFA836117B1B572FAE4713F200567' => 'b05be3e17bb9987ffb368696ee916dd9b9c2f9b3',
          '000001BCBC3B7C8C6E5FC59B686D3568132D218C' => 'd09565280ebae0a37ca9385bc39c0a777a446554'
        };
Required sources :
$VAR1 = {
          '50edd315b9217345b1728c38b02657df42043197' => 1,
          '36bed8bdb6d66fb67f409166f5db64b02199812f' => 1,
          '55b8ece03f4935f9be667e332d52f7db3e17b809' => 1,
          'b05be3e17bb9987ffb368696ee916dd9b9c2f9b3' => 1,
          '67c0da2da88a23a803733cea951e84974b34d029' => 1,
          '2adeac692d450c54f8830014ee6cbe3a958c1e60' => 1,
          'd09565280ebae0a37ca9385bc39c0a777a446554' => 1,
          '3c4b0a3c1acf6e03111805a0d8b4e879df112b7a' => 1,
          '691845459c0ad35b28cce4dffc0e3ee8912fb0f5' => 1,
          '0c5e6cdb06c52160ded398d17392246269165e0a' => 1,
          '2f214516cdcab089e83f3e5094928fe9611f2f51' => 1,
          'cd15550344b5b9c2785a13ef9583015f267ad667' => 1
        };


Remaining keys:
$VAR1 = {};