in reply to Heap sorting in perl
#!/usr/bin/perl
use strict;
use warnings;
my @heap;
sub heapify;
sub heapify {
my $idx = shift;
my $min = $idx;
for my $try (2 * $idx + 1, 2 * $idx + 2) {
$min = $try if $try < @heap && $heap [$try] < $heap [$min]
}
return if $min == $idx;
@heap [$idx, $min] = @heap [$min, $idx];
heapify $min;
}
sub extract_min {
return unless @heap;
my $min = $heap [0];
my $tmp = pop @heap;
if (@heap) {
$heap [0] = $tmp;
heapify 0;
}
return $min;
}
#
# First argument the number of smallest elements to be returned.
# Then the list to find the elements in.
#
sub smallest {
my $k = shift;
@heap = @_;
for (my $i = int (@heap / 2); $i ;) {
heapify $i;
}
my @result;
push @result => extract_min while @heap && $k ;
@result;
}
__END__
The running time of this is O (N + k log N), where N is the
size of the set, and k the number of elements to be returned.
Abigail
