Prime Number of Set Bits in Binary Representation

class Solution {
    public int countPrimeSetBits(int left, int right) {
        // 32.. 1 32 -- > 2,3,5,7,11,13..
        HashSet<Integer> hset = new HashSet<>(
            Arrays.asList(2,3,5,7,11,13,17,19,31)
        );
        int ans = 0;
        for(int i=left; i<=right; i++) {
            // O(right-left)*32 // O(1)
            int setbits = Integer.bitCount(i);
            if(hset.contains(setbits))
                ans++;
        }
        return ans;
    }
}