So close...

Author: mrusnaczyk

Challenges_VII/Carmichael_Numbers/Main.java

@@ -0,0 +1,60 @@
+package Challenges_VII.Carmichael_Numbers;
+
+import java.math.BigInteger;
+import java.util.HashMap;
+import java.util.Scanner;
+
+public class Main {
+	
+	public static final int MAX = 65001;
+	public static HashMap<String,Integer> primeHash;
+
+	public static void main(String[] args) {
+		Scanner s = new Scanner(System.in);
+		primeHash = new HashMap<String, Integer>();
+		int next;
+		genPrimes();
+		
+		while((next = s.nextInt()) != 0){
+			BigInteger randNum = BigInteger.valueOf((int) (Math.random() * (next - 1)) + 2);
+			BigInteger fermatTest = randNum.pow(next).mod(BigInteger.valueOf(next));
+			if(fermatTest.equals(randNum) && primeHash.get(String.valueOf(next)) == null){
+				System.out.println("The number " + next + " is a Carmichael number.");
+			}else{
+				System.out.println(next + " is normal.");
+			}
+		}
+		s.close();
+		System.exit(0);
+
+	}
+	
+	
+	public static void genPrimes(){
+		
+	    boolean[] sieve = new boolean[MAX+1]; 
+	    sieve[0] = true; 
+	    sieve[1] = true; 
+	    sieve[2] = false;
+
+	    for(int i = 4; i <= MAX; i+=2)
+	    	sieve[i] = true;
+	    
+	    for(int i = 3; i < (int)Math.sqrt(MAX)+1; i+=2)
+	    {
+	        if(!sieve[i])
+	        {
+	            for(int j = i*i; j <= MAX; j+=i)
+	            	sieve[j] = true;
+	        }
+	    }
+	    
+	    for(int b = 0; b < sieve.length; b++){
+	    	if(!sieve[b]){
+	    		primeHash.put(String.valueOf(b), b);
+	    	}
+	    }
+
+	}
+
+}