#!/usr/bin/perl                                                                                                   

@bigrams = ();

while (<>) {
    chomp;
    push @words, split( /\s+/, $_ );
}

for ( $i = 0 ; $i < $#words ; $i++ ) {
    $bigram = $words[$i] . $words[ $i + 1 ];
    $found  = -1;
    for ( $index = 0 ; $index <= $#bigrams ; $index++ ) {
        {
            if ( $bigrams[$index] eq $bigram ) {
                $found = $index;
            }
        }
    }
    if ( $found > -1 ) {
        $bigramfrequency[$found]++;
    }
    else {
        push( @bigrams, $bigram );
        $bigramfrequency[$#bigrams]++;
    }
}

print "Bigrams\n";

for ( $index = 0 ; $index < @bigrams ; $index++ ) {
    print "$bigrams[$index] : $bigramfrequency[$index]\n";
}