S-12345-add-new-algo

src/main/java/com/williamfiset/algorithms/math/RandomizedIsPrime.java

@@ -0,0 +1,54 @@
+package com.williamfiset.algorithms.math;
+
+import java.util.Scanner;
+
+public class RandomizedIsPrime{
+
+    private static final Integer ITERATION = 20;
+
+    public static boolean isPrime(long n, int iteration) {
+        long a;
+
+        long up = n - 2;
+        long down = 2;
+        for (int i = 0; i < iteration; i++) {
+            a = (long) Math.floor(Math.random() * (up - down + 1) + down);
+            if (modPow(a, n - 1, n) != 1) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    /**
+     * *
+     *
+     * @param a basis
+     * @param b exponent
+     * @param c modulo
+     * @return (a ^ b) mod c
+     */
+    private static long modPow(long a, long b, long c) {
+        long res = 1;
+        for (int i = 0; i < b; i++) {
+            res *= a;
+            res %= c;
+        }
+        return res % c;
+    }
+
+    public static void main(String[] args) {
+        Scanner scanner = new Scanner(System.in);
+
+        System.out.print("Enter a number: ");
+
+        long n = scanner.nextInt();
+        if (isPrime(n, ITERATION)) {
+            System.out.println(n + " is Prime");
+        } else {
+            System.out.println(n + " isn't Prime");
+        }
+
+    }
+
+}