Data Update

Task/Descending-primes/Java/descending-primes.java

@@ -0,0 +1,48 @@
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+public final class DescendingPrimes {
+
+	public static void main(String[] aArgs) {
+		List<Integer> allNumbersStrictlyDescendingDigits = new ArrayList<Integer>(512);
+		for ( int i = 0; i < 512; i++ ) {
+		    int number = 0;
+		    int temp = i;
+		    int digit = 9;
+		    while ( temp > 0 ) {
+		        if ( temp % 2 == 1 ) {
+		        	number = number * 10 + digit;
+		        }
+		        temp >>= 1;
+		        digit -= 1;
+		    }
+		    allNumbersStrictlyDescendingDigits.add(number);
+		}
+
+		Collections.sort(allNumbersStrictlyDescendingDigits);
+		
+		int count = 0;
+		for ( int number : allNumbersStrictlyDescendingDigits ) {
+		    if ( isPrime(number) ) {
+		        System.out.print(String.format("%9d%s", number, ( ++count % 10 == 0 ? "\n" : " " )));
+		    }
+		}
+		System.out.println(System.lineSeparator());
+		System.out.println("There are " + count + " descending primes.");	
+	}
+	
+	private static boolean isPrime(int aNumber) {
+	    if ( aNumber < 2 || ( aNumber % 2 ) == 0 ) {
+	    	return aNumber == 2;
+	    }
+	
+	    for ( int divisor = 3; divisor * divisor <= aNumber; divisor += 2 ) {
+	    	if ( aNumber % divisor == 0 ) {
+	    		return false;
+	    	}
+	    }
+	    return true;
+	}
+
+}