49 lines
1.0 KiB
Java
49 lines
1.0 KiB
Java
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);
|
|
}
|
|
}
|