3616、n的幂

package cn.fansunion.leecode.math;

/**

 * @author [email protected]

 *

 *         2022-2-23

 */

public class MathPower {

    /**

     * 判定一个数n是否为某个数a的b次方。PowerOfThree,PowerOfFour，本质都是PowerOfN。

     *

     * @param num

     * @param n

     */

    public boolean powerOfN(int n, int a) {

        if (n <= 0) {

            return false;

        }

        if (n == 1) {

            return true;

        }

        // >=a

        while (n >= a) {

            if (n % a == 0) {

                n = n / a;

            } else {

                return false;

            }

        }

        // 1

        return n == 1;

    }

    /**

     * Math.pow(a,b)，支持整数,b>=0;2的3次方=8

     *

     * @param a

     * @param b

     * @return

     */

    public int pow(int a, int b) {

        if (b < 0) {

            throw new IllegalArgumentException("b<0");

        }

        if (b == 0) {

            return 1;

        }

        int n = 1;

        for (int index = 0; index < b; index++) {

            n = n * a;

        }

        return n;

    }

}

package test.leecode.math;

import org.junit.Assert;

import org.junit.Test;

import cn.fansunion.leecode.math.MathPower;

/**

 * @author [email protected]

 *

 *         2022-2-23

 */

public class MathPowerTest {

    @Test

    public void test() {

        MathPower mp = new MathPower();

        // 4

        Assert.assertTrue(mp.powerOfN(16, 4));

        Assert.assertTrue(mp.powerOfN(256, 4));

        Assert.assertTrue(mp.powerOfN(4, 4));

        Assert.assertTrue(mp.powerOfN(1, 4));

        Assert.assertFalse(mp.powerOfN(-1, 4));

        Assert.assertFalse(mp.powerOfN(3, 4));

        Assert.assertFalse(mp.powerOfN(257, 4));

        // 3

        Assert.assertTrue(mp.powerOfN(27, 3));

        Assert.assertTrue(mp.powerOfN(9, 3));

        Assert.assertTrue(mp.powerOfN(3, 3));

        Assert.assertTrue(mp.powerOfN(1, 3));

        Assert.assertFalse(mp.powerOfN(-1, 3));

        Assert.assertFalse(mp.powerOfN(-3, 3));

        Assert.assertFalse(mp.powerOfN(257, 3));

    }

    @Test

    public void testPow() {

        MathPower mp = new MathPower();

        Assert.assertEquals(1, mp.pow(1, 4));

        Assert.assertEquals(16, mp.pow(2, 4));

        Assert.assertEquals(81, mp.pow(3, 4));

        Assert.assertEquals(625, mp.pow(5, 4));

        Assert.assertEquals(27, mp.pow(3, 3));

        Assert.assertEquals(9, mp.pow(3, 2));

        Assert.assertEquals(1, mp.pow(3, 0));

        Assert.assertEquals(1, mp.pow(4, 0));

    }

}