#!/usr/bin/env perl
use strict;
use warnings;
use autodie;
use feature 'say';

my @trigrams;
my @trigramfrequency;
my @words;
while (<DATA>) {
    push @words, split /\s/;
}
for ( my $i = 0 ; $i < $#words - 1 ; $i++ ) {
    my $trigram = $words[$i] . $words[ $i + 1 ] . $words[ $i + 2 ];
    my $found   = -1;

    if (@trigrams) {
      SEARCHtrigramINDEX:
        for ( my $index = 0 ; $index <= $#trigrams ; $index++ ) {
            if ( $trigrams[$index] eq $trigram ) {
                $found = $index;
                last SEARCHtrigramINDEX;
            }
        }
    }

    if ( $found > -1 ) {
        $trigramfrequency[$found]++;
    }
    else {
        push @trigrams, $trigram;
        $trigramfrequency[$#trigrams]++;
    }
}
print "trigram frequencies in your text:\n";

for ( my $index = 0 ; $index <= @trigrams ; $index++ ) {
    print "$trigrams[$index] $trigramfrequency[$index]\n";
}
__DATA__
hai! how are you?
will you come to Canada this weekend?
hai! Hello! I am fine.
No I am not coming to Canada this weekend.
I will come to Canada next week:
I will meet you next month at Canada