Well, in that case...

my (%edge, @seen);

while (<STDIN>) {
    $seen[$2]++ or push @{$edge{$1}}, $2 if /(\d+)\D+(\d+)/;
    # push @{$edge{$1}}, $2 if /(\d+)\D+(\d+)/ and not $seen[$2]++;
}

[download]

— Arien

Edit: added the commented alternative.

In reply to Re(3): Putting it together by Arien
in thread H of A optimization by abitkin

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