my (%edgeHash,@alreadySeen);

while(<STDIN>){

    # simpler regexp
    if(/(\d+)\D+(\d+)/){
        # don't use '$a' and '$b'!
        # and don't quote "$vars"
        # in fact you can keep $1 and $2
        push @{$edgeHash{$1}}, $2 unless
              $alreadySeen[int($2)]++;
    }
}