Question

What is the best algorithm/approach to iterate through a file with numerous lines of Countries and printing out the country with the most occurrences?

Each line is a string and only contains a country name on each line.

Assume there could be 1 billion distinct countries. (Countries is a bad example)

United States
Iran
India
United States
China
Iran
....
....
Canada //1 billionth line

Answer 1

# Count the unique elements.
my %hash;
while(<>) {
    chomp;
    $hash{$_}++;
}

# Find the key with the largest value.
sub largest_value {
    my $hash = shift;

    my ($big_key, $big_val) = each %$hash;

    while (my ($key, $val) = each %$hash) {
        if ($val > $big_val) {
            $big_key = $key;
            $big_val = $val;
        }
    }

    return $big_key;
}

print largest_value(\%hash);