#!/usr/local/bin/perl -sl
use strict;
use warnings;

local $, = ' ';

{
    no strict 'refs';
    no warnings 'uninitialized';

    my $C = 0;

    sub query{
        my $i = shift;
        my $x = ${"a_$i"};
        return (0 <= $x and $x < $C and ${"b_$x"} == $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 ) ) {
            $C--;
            my $x = ${"a_$i"};
            my $y = ${"b_$C"};
            ${"b_$x"} = $y;
            ${"a_$y"} = $x;
        }
    }

    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 exists

print "\nQuery after deleting the rest";
printf "%5d : %s\n", $_, query( $_ ) for @numbers;

--------

Query before insert
56155 : 0
20459 : 0
15365 : 0
55048 : 0
47183 : 0
49635 : 0
32939 : 0
17320 : 0
54582 : 0
62554 : 0

Query after insert
56155 : 1
20459 : 1
15365 : 1
55048 : 1
47183 : 1
49635 : 1
32939 : 1
17320 : 1
54582 : 1
62554 : 1

Query after deleting half
56155 : 0
20459 : 0
15365 : 0
55048 : 0
47183 : 0
49635 : 1
32939 : 1
17320 : 1
54582 : 1
62554 : 1

Query after deleting the rest
56155 : 0
20459 : 0
15365 : 0
55048 : 0
47183 : 0
49635 : 0
32939 : 0
17320 : 0
54582 : 0
62554 : 0