my %counts = (
     "Adam"      => { "201708"   => 1, "201703" => 1, "201804" => 1, "201603" => 1, "201705" => 1, "201702" => 1, "201608" => 1, "201704" => 1,},
     "Sam" => { "201803"  => 1,  "201801" => 1 },
 );

use List::UtilsBy 'max_by';
foreach my $key ( keys %counts ) {
    my $subhash = $counts{$key};
    my $maximal = max_by { $subhash->{$_} } keys %$subhash;
    print "$key, $maximal\n";
}


use List::UtilsBy 'min_by';
foreach my $key ( keys %counts ) {
    my $subhash = $counts{$key};
    my $minimal = max_by { $subhash->{$_} } keys %$subhash;
    print "$key, $minimal\n";
}