use strict;

my @array = (1, 5, 4, 10, 20, 2, 1, 3, 7);
my @hi = (0) x 3;                # '0' assumes positive #'s

foreach (@array) {
   $_ <= $hi[0] and next;
   @hi = (sort $a<=>$b, @hi, $_)[-3..-1];
}

print "@hi";