Added Binary Exponentiation Fixes:TheAlgorithms#1943 (TheAlgorithms#1945)

* Added Binary Exponentiation Fixes:TheAlgorithms#1943

* tests added in Binary Exponentation TheAlgorithms#1945

* Assertion Added

Author: Lakhan-Nad

Maths/BinaryPow.java

@@ -0,0 +1,46 @@
+package Maths;
+
+public class BinaryPow {
+  /**
+   * Calculate a^p using binary exponentiation
+   * [Binary-Exponentiation](https://cp-algorithms.com/algebra/binary-exp.html)
+   *
+   * @param a the base for exponentiation
+   * @param p the exponent - must be greater than 0
+   * @return a^p
+   */
+  public static int binPow(int a, int p) {
+    int res = 1;
+    while (p > 0) {
+      if ((p & 1) == 1) {
+        res = res * a;
+      }
+      a = a * a;
+      p >>>= 1;
+    }
+    return res;
+  }
+
+  /** 
+   * Function for testing binary exponentiation
+   * @param a the base 
+   * @param p the exponent
+   */
+  public static void test(int a, int p) { 
+    int res = binPow(a, p);
+    assert res == (int) Math.pow(a, p) : "Incorrect Implementation";
+    System.out.println(a + "^" + p + ": " + res);
+  }
+
+  /** Main Function to call tests
+   * 
+   * @param args System Line Arguments
+   */
+  public static void main(String[] args) {
+    // prints 2^15: 32768
+    test(2, 15); 
+
+    // prints 3^9: 19683
+    test(3,9);
+  }
+}