LC 762. Prime Number of Set Bits in Binary Representation - Weekly Contest 67 - LeetCode

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 1s 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 = 10
Output: 4
Explanation:
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 = 15
Output: 5
Explanation:
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.

	class Solution {
	/**
	* @param L
	* @param R
	* @return
	*/
	public int countPrimeSetBits(int L, int R) {
	if (L > R) {
	return 0;
	}
	// core logic
	int counter = 0;
	for (int i = L; i <= R; i++) {
	if (isPrime(numberOfBits(i))) {
	counter++;
	}
	}
	return counter;
	}
	private int numberOfBits(int i) {
	int counter = 0;
	while (i > 0) {
	counter += i % 2;
	i /= 2;
	}
	return counter;
	}
	private static HashSet<Integer> primeSet = new HashSet<>();
	static {
	{
	primeSet.add(2);
	primeSet.add(3);
	primeSet.add(5);
	primeSet.add(7);
	primeSet.add(11);
	primeSet.add(13);
	primeSet.add(17);
	primeSet.add(19);
	primeSet.add(23);
	primeSet.add(29);
	primeSet.add(31);
	}
	}
	private boolean isPrime(int i) {
	return primeSet.contains(i);
	}
	}

view raw 762. Prime Number of Set Bits in Binary Representation.java hosted with ❤ by GitHub