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