Given two integers `L`

and `R`

, find the count of numbers in the range `[L, R]`

(inclusive) having a prime number of set bits in their binary representation.

(Recall that the number of set bits an integer has is the number of `1`

s present when written in binary. For example, `21`

written in binary is `10101`

which has 3 set bits. Also, 1 is not a prime.)

**Example 1:**

Input:L = 6, R = 10Output:4Explanation:6 -> 110 (2 set bits, 2 is prime) 7 -> 111 (3 set bits, 3 is prime) 9 -> 1001 (2 set bits , 2 is prime) 10->1010 (2 set bits , 2 is prime)

**Example 2:**

Input:L = 10, R = 15Output:5Explanation:10 -> 1010 (2 set bits, 2 is prime) 11 -> 1011 (3 set bits, 3 is prime) 12 -> 1100 (2 set bits, 2 is prime) 13 -> 1101 (3 set bits, 3 is prime) 14 -> 1110 (3 set bits, 3 is prime) 15 -> 1111 (4 set bits, 4 is not prime)

**Note:**

`L, R`

will be integers`L <= R`

in the range`[1, 10^6]`

.`R - L`

will be at most 10000.

```
struct Solution;
use std::collections::HashSet;
use std::iter::FromIterator;
impl Solution {
fn count_prime_set_bits(l: i32, r: i32) -> i32 {
let mut res = 0;
let hs: HashSet<i32> = HashSet::from_iter(vec![2, 3, 5, 7, 11, 13, 17, 19]);
for i in l..=r {
let ones = i.count_ones() as i32;
if hs.contains(&ones) {
res += 1;
}
}
res
}
}
#[test]
fn test() {
assert_eq!(Solution::count_prime_set_bits(6, 10), 4);
assert_eq!(Solution::count_prime_set_bits(10, 15), 5);
}
```