Data commit

Task/Emirp-primes/Java/emirp-primes.java

@@ -0,0 +1,54 @@
+public class Emirp{
+	
+	//trivial prime algorithm, sub in whatever algorithm you want
+	public static boolean isPrime(long x){
+		if(x < 2) return false;
+		if(x == 2) return true;
+		if((x & 1) == 0) return false;
+		
+		for(long i = 3; i <= Math.sqrt(x);i+=2){
+			if(x % i == 0) return false;
+		}
+		
+		return true;
+	}
+	
+	public static boolean isEmirp(long x){
+		String xString = Long.toString(x);
+		if(xString.length() == 1) return false;
+		if(xString.matches("[24568].*") || xString.matches(".*[24568]")) return false; //eliminate some easy rejects
+		long xR = Long.parseLong(new StringBuilder(xString).reverse().toString());
+		if(xR == x) return false;
+		return isPrime(x) && isPrime(xR);
+	}
+	
+	public static void main(String[] args){
+		int count = 0;
+		long x = 1;
+		
+		System.out.println("First 20 emirps:");
+		while(count < 20){
+			if(isEmirp(x)){
+				count++;
+				System.out.print(x + " ");
+			}
+			x++;
+		}
+		
+		System.out.println("\nEmirps between 7700 and 8000:");
+		for(x = 7700; x <= 8000; x++){
+			if(isEmirp(x)){
+				System.out.print(x +" ");
+			}
+		}
+		
+		System.out.println("\n10,000th emirp:");
+		for(x = 1, count = 0;count < 10000; x++){
+			if(isEmirp(x)){
+				count++;
+			}
+		}
+		//--x to fix the last increment from the loop
+		System.out.println(--x);
+	}
+}