Added MillerRabin

MillerRabin/MillerRabin.iml

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<module type="JAVA_MODULE" version="4">
+  <component name="NewModuleRootManager" inherit-compiler-output="true">
+    <exclude-output />
+    <content url="file://$MODULE_DIR$">
+      <sourceFolder url="file://$MODULE_DIR$/src" isTestSource="false" />
+    </content>
+    <orderEntry type="inheritedJdk" />
+    <orderEntry type="sourceFolder" forTests="false" />
+  </component>
+</module>
+

MillerRabin/src/com/company/Main.java

@@ -0,0 +1,83 @@
+package com.company;
+
+import java.util.Scanner;
+import java.util.concurrent.ThreadLocalRandom;
+
+/* Code developed by Eryk Szlachetka
+*  Implementation of Miller-Rabin algorithm,
+*  to check if the number is prime or not.
+*  If the algorithm returns Composite then the number is probably prime.
+*  If the algorithm returns inconclusive, then it is not prime.
+*/
+
+public class Main {
+
+    public static void main(String[] args) {
+
+        String prime = "";
+        long n;
+        boolean isPrime;
+
+        Scanner scan = new Scanner(System.in);
+        System.out.println("Enter a number to check if it is prime: ");
+        n = scan.nextLong();
+        System.out.println("Checking...\n");
+        isPrime = checkIfPrime(n);
+
+        if(isPrime){
+            prime = "Composite";
+        }else{
+            prime = "Inconclusive";
+        }
+
+        System.out.println("The number: " + n + " is: " + prime);
+
+    }
+
+    private static boolean checkIfPrime(long n){
+
+        // Return false if n is 0 or 1 as its not prime
+        if(n == 0 || n == 1){
+            return false;
+        }
+        // Return true if n is 2, as it is prime
+        if(n == 2){
+            return true;
+        }
+        // If its an even number other than 2 then return false.
+        if(n % 2 == 0){
+            return false;
+        }
+
+
+        // Find integers k, q with k > 0, q is odd so that (n - 1 = 2^k q)
+        long q = n-1;
+        int k = 0;
+
+        while(q % 2 == 0){ // while q is odd
+            q = q/2; // divide q by 2
+            k++;     // increment k
+        }
+        // Select random integer a where 1 < a < n-1
+        long a = ThreadLocalRandom.current().nextLong(1, (n-1));
+
+        // If a^q mod n == 1 then return "inconclusive"
+        if(((a^q) % n) == 1){
+            return false;
+        }
+
+        for(int j =0; j < k-1; j++){
+            // if a^((2^j)q) mod n == n - 1 then return "inconclusive"
+            long power = 2^j * q;
+            long res = a^power;
+
+            if(res % n == n-1) {
+                return false;
+            }
+        }
+        // Return "composite"
+        return true;
+    }
+}
+
+