PerfectPowerTest.java

package com.michaelmidura.kataday.day029;

import java.util.Random;

import org.junit.Test;

import static java.lang.Math.log;
import static org.junit.Assert.assertArrayEquals;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertNull;
import static org.junit.Assert.assertNotNull;

public class PerfectPowerTest {

	@Test
	public void test0() {
		assertNull("0 is not a perfect number", PerfectPower.isPerfectPower(0));
	}

	@Test
	public void test1() {
		assertNull("1 is not a perfect number", PerfectPower.isPerfectPower(1));
	}

	@Test
	public void test2() {
		assertNull("2 is not a perfect number", PerfectPower.isPerfectPower(2));
	}

	@Test
	public void test3() {
		assertNull("3 is not a perfect number", PerfectPower.isPerfectPower(3));
	}

	@Test
	public void test4() {
		assertArrayEquals("4 = 2^2", new int[]{2, 2}, PerfectPower.isPerfectPower(4));
	}

	@Test
	public void test5() {
		assertNull("5 is not a perfect power", PerfectPower.isPerfectPower(5));
	}

	@Test
	public void test8() {
		assertArrayEquals("8 = 2^3", new int[]{2, 3}, PerfectPower.isPerfectPower(8));
	}

	@Test
	public void test9() {
		assertArrayEquals("9 = 3^2", new int[]{3, 2}, PerfectPower.isPerfectPower(9));
	}

	@Test
	public void testUpTo500() {
		int[] pp = {4, 8, 9, 16, 25, 27, 32, 36, 49, 64, 81, 100, 121, 125, 128, 144, 169, 196, 216, 225, 243, 256, 289, 324, 343, 361, 400, 441, 484};
		for (int i : pp) assertNotNull(i + " is a perfect power", PerfectPower.isPerfectPower(i));
	}

	@Test
	public void testRandomPerfectPowers() {
		Random rnd = new Random();
		for (int i = 0; i < 100; i++) {
			System.out.println(i);
			int m = rnd.nextInt(254) + 2;
			int k = (int) (rnd.nextDouble() * (log(Integer.MAX_VALUE) / log(m) - 2.0) + 2.0);
			int l = ipow(m, k);
			int[] r = PerfectPower.isPerfectPower(l);
			assertNotNull(l + " is a perfect power", r);
			assertEquals(r[0] + "^" + r[1] + "!=" + l, l, ipow(r[0], r[1]));
		}
	}

	@Test
	public void testRandomNumbers() {
		Random rnd = new Random();
		for (int i = 0; i < 100; i++) {
			int l = rnd.nextInt(Integer.MAX_VALUE);
			int[] r = PerfectPower.isPerfectPower(l);
			if (r != null) assertEquals(r[0] + "^" + r[1] + "!=" + l, l, ipow(r[0], r[1]));
		}
	}

	private static int ipow(int b, int e) {
		int p = 1;
		for (; e > 0; e >>= 1) {
			if ((e & 1) == 1) p *= b;
			b *= b;
		}
		return p;
	}

}