#! perl -slw
use strict;
local $, = ' ';

my( $A, $B, $C ) = ( {}, [], 0 );

sub query{
    my $i = shift;
    return ( exists $A->{ $i } and 0 <= $A->{ $i } and $A->{ $i } < $C
+ and $B->[ $A->{ $i } ] == $i ) ? 1 : 0;
}

sub insert{
    my $i = shift;
    if( !query( $i ) ) {
        $B->[ $C ] = $i;
        $A->{ $i } = $C;
        $C++
    }
}

sub del{
    my $i = shift;
    if( query( $i ) ) {
        my $a = $A->{ $i };
        my $b = $B->[ --$C ];
        $B->[ $a ] = $b;
        $A->{ $b } = $a;
    }
}

sub clear{
    $C = 0;
}

my @numbers = map{ int rand( 2**16 ) } 1 .. 10;
print 'Query before insert';
printf "%5d : %s\n", $_, query( $_ ) for @numbers;
insert $_ for @numbers;
print "\nQuery after insert";
printf "%5d : %s\n", $_, query( $_ ) for @numbers;
del $_ for @numbers[ 0..4 ]; ## Delete half
print "\nQuery after deleting half";
printf "%5d : %s\n", $_, query( $_ ) for @numbers;
del $_ for @numbers; ## Delete them all regardless if they still exist
+s
print "\nQuery after deleting the rest";
printf "%5d : %s\n", $_, query( $_ ) for @numbers;
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