Question $3$: Design a data structure where the keys are positive integers. The data

structure should support the following operations:

$($a$)$ Insert$($S$,$ x$)$: Insert x into the data structure S$.$

$($b$)$ Delete$($S$,$ x$)$: Delete x from the data structure S$.$

$($c$)$ Search$($S$,$ x$)$: Search for x in the data structure S$.$

$($d$)$ F ind $$ Even$($S$)$: Find the number of even elements in the data structure S$.$