PrimeCount.java

public class PrimeCount {
	
//	Write a function named primeCount with signature int primeCount(int start, int end);
//	The function returns the number of primes between start and end inclusive.
//	Recall that a prime is a positive integer greater than 1 whose only integer factors are 1 and itself.
//
//	Examples
//	 -------------|------------|---------|------------------------------------------------------------------
//	| if start is | and end is | return  | reason                                                           |
//	|-------------|------------|---------|------------------------------------------------------------------|
//	| 10          | 30         | 6       | The primes between 10 and 30 inclusive are 11,13,17,19,23 and 29 |
//	|-------------|------------|---------|------------------------------------------------------------------|
//	| 11          | 29         | 6       | The primes between 11 and 29 inclusive are 11,13,17,19,23 and 29 |
//	|-------------|------------|---------|------------------------------------------------------------------|
//	| 20          | 22         | 0       | 20,21, and 22 are all non-prime                                  |
//	|-------------|------------|---------|------------------------------------------------------------------|
//	| 1           | 1          | 0       | By definition, 1 is not a prime number                           |
//	|-------------|------------|---------|------------------------------------------------------------------|
//	| 5           | 5          | 1       | 5 is a prime number                                              |
//	|-------------|------------|---------|------------------------------------------------------------------|
//	| 6           | 2          | 0       | start must be less than or equal to end                          |
//	|-------------|------------|---------|------------------------------------------------------------------|
//	| -10         | 6          | 3       | primes are greater than 1. 2, 3 and 5 are prime                  |
//	 -------------|------------|---------|------------------------------------------------------------------

	
	static int primeCount(int start,int end) {
		
		int count = 0;
		
		for (int i=start;i<=end;i++) {
			if (isPrime(i) == true) {
				count++;
			}
		}
		
		return count;
	}
	
	static boolean isPrime(int n) {
		if (n < 2) return false; 
		
		for (int i = 2;i<n;i++){
			if (n % i == 0) {
				return false;
			}
		}
		
		return true;
	}
	
	static void primeCountTest() {
		System.out.println(primeCount(10, 30));
		System.out.println(primeCount(11, 29));
		System.out.println(primeCount(20, 22));
		System.out.println(primeCount(1, 1));
		System.out.println(primeCount(5, 5));
		System.out.println(primeCount(6, 2));
		System.out.println(primeCount(-10, 6));
	}
	
	
	public static void main(String[] args) {
		primeCountTest();
	}
}