text: now if primes [ mid ] < n and primes [ mid + 1 ] > n that means we reached at nearest prime
code: if ( $ primes [ $ mid ] < $ n && $ primes [ $ mid + 1 ] > $ n ) return $ primes [ $ mid ] ; if ( $ n < $ primes [ $ mid ] ) return binarySearch ( $ left , $ mid - 1 , $ n ) ; else return binarySearch ( $ mid + 1 , $ right , $ n ) ; } return 0 ; }