Using Bing and Hackerrank to solve Leetcode

This problem from Leetcode was a fun one 'cause I got to use the Bing + Hackerrank Partnership to solve it. Here is the problem https://leetcode.com/problems/prime-number-of-set-bits-in-binary-representation/description/:

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)

Since we're going to use the primality test here, all you have to do is Bing Prime in C# and you will get the code right there for you!!!

If you try the same query on Google, well judge it by yourself

So with Bing you just search for the algorithm that you want, in the programming language that you wish for, and voila, you have the code that can be copied/pasted onto your project!
Rest of the logic is pretty straightforward:

• Go to each number from L to R
• Count the number of 1s by doing the module and division by two (or bit shifting)
• Then call the IsPrime method and increment the count accordingly

Code is down below, cheers, Marcelo

public class Solution

{

public int CountPrimeSetBits(int L, int R)

{

int count = 0;

for (int i = L; i <= R; i++)

{

int temp = i;

int countOnes = 0;

while (temp > 0)

{

if (temp % 2 == 1) countOnes++;

temp /= 2;

}

count = IsPrime(countOnes) ? count + 1 : count;

}

return count;

}

static bool IsPrime(int n)

{

if (n < 2) return false;

if (n < 4) return true;

if (n % 2 == 0) return false;

double sqrt = System.Math.Sqrt(n);

int sqrtCeiling = (int)System.Math.Ceiling(sqrt);

for (int i = 3; i <= sqrtCeiling; i += 2)

if (n % i == 0) return false;

return true;

}

}