【笔试】29、数值的整数次方

/**
 *题目：实现函数double Power(double base, int exponent),求base的exponent次方。不得使用库函数，同时不需要考虑大数问题
 *时间：2015年8月28日10:48:28
 *文件：MyPow.java
 *作者：cutter_point
 */
package bishi.Offer50.y2015.m08.d28;

import org.junit.Test;

public class MyPow
{
	/**
	 * 求一个数的exponent次方
	 * @param base
	 * @param exponent
	 * @return
	 */
	public double power(double base, int exponent)
	{
		if(this.equal(base, 0.0))
			return 0;
		else if(this.equal(exponent, 0.0))
			return 1;
		
		int absExponent = exponent;
		boolean isFu = false;	//是否是负数
		if(exponent < 0)
		{
			isFu = true;
			absExponent = -exponent;
		}//if
		
		double result = absPower(base, absExponent);
		if(isFu)
		{
			result = 1 / result;
		}//if
		
		return result;
	}
	
	/**
	 * 当指数是正数的时候
	 * @param base
	 * @param absExponent
	 * @return
	 */
	public double absPower(double base, int absExponent)
	{
		double result = 1.0;
		for(int i = 1; i <= absExponent; ++i)
			result *= base;
		return result;
	}
	
	/**
	 * 更快的算法
	 * @param base
	 * @return
	 */
	public double absPower2(double base, int absException)
	{
		if(absException == 0)
			return 1;
		else if(absException == 1)
			return base;
		
		double result = absPower2(base, absException >> 1);
		result *= result;
		//判断奇偶
		if((absException & 0x1) == 1)
		{
			result *= base;
		}
		
		return result;
	}
	
	/**
	 * 计算机中单纯的result == 0并不能好好判断这两个数是否一样，float和double类型的数在计算机中表示是有误差的
	 * @param num1
	 * @param num2
	 * @return
	 */
	public boolean equal(double num1, double num2)
	{
		double result = num1 - num2;
		if(result < 0.0000001 && result > -0.0000001)
		{
			return true;
		}
		else
			return false;
	}
	
	public static void test(double base, int exponent)
	{
		MyPow mp = new MyPow();
		double time1 = System.currentTimeMillis();
		System.out.println(mp.power(base, exponent));
		double time2 = System.currentTimeMillis();
		System.out.println("运行时间：" + (time2 - time1));
		System.out.println(mp.absPower2(base, exponent));
		double time3 = System.currentTimeMillis();
		System.out.println("运行时间：" + (time3 - time2));
	}
	
	@Test
	public void test1()
	{
		test(0, 10);
	}
	
	@Test
	public void test2()
	{
		test(65, 10);
	}
	
	public static void main(String[] args)
	{
		// TODO Auto-generated method stub

	}

}