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Check if a number is prime (JAVA)
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package InterviewProject; | |
import java.util.ArrayList; | |
import java.util.List; | |
import java.util.stream.Collectors; | |
import java.util.stream.IntStream; | |
public class InterviewMain { | |
public static void main(String[] args) { | |
// Prime Number detector | |
// Print out all number between 1 and 100 | |
List<Integer> range = IntStream.rangeClosed(1, 100) | |
.boxed().collect(Collectors.toList()); | |
System.out.println("Opening range of numbers:"); | |
System.out.println(range); | |
ArrayList<Integer> primeNumbers = new ArrayList<Integer>(); | |
for (int i = 1; i < 101; i++) { | |
if (isPrime(i)) { | |
primeNumbers.add(i); | |
}; | |
} | |
System.out.println("Prime range of numbers:"); | |
System.out.println(primeNumbers); | |
} | |
public static boolean isPrime(Integer n) { | |
// def: only div by 1 and itself | |
// edge cases | |
if (n <= 1) { | |
return false; | |
} | |
if (n <= 3) { | |
return true; | |
} | |
// we can skip the middle five numbers | |
if (n % 2 == 0 || n % 3 == 0) { | |
return false; | |
} | |
// check from 5 to n | |
for (int i = 5; i * i <= n; i = i + 6) { | |
if (n % i == 0 || n % (i + 2) == 0) { | |
return false; | |
} | |
} | |
return true; | |
} | |
} |
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