To deal with leap years, you could make the @days array like this:

my @days = (
    [ qw(31 28 31 30 31 30 31 31 30 31 30 31) ], # non-leap
    [ qw(31 29 31 30 31 30 31 31 30 31 30 31) ]  # leap
)
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A function to return 0 when a gives year is not a leap year, and 1 if it is:

sub leap {
    my $y = shift;
    return ($y % 4 == 0 && $y % 100 != 0) || $y % 400 == 0;
}
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and you can use it like

my $leap = leap($y);

...

$days[$leap][$m]
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Arjen