剑指offer面试题11 数值的整数次方

考察点

知识点

比较俩个浮点数是否相等的方法是判断他俩的差的绝对值是否小于一个很小的数

题目

分析
这道题目是一道比较常规的题目，把异常输入，各种可能的输入都考虑到就可以了。要考虑到指数和基数同时为正，同时为负，指数为正基数为负以及指数为负基数为正的情况

public class Eleven {
	public static void main(String[] args) {
		System.out.println(power(2,3));
		System.out.println(power(2,-3));
		System.out.println(power(-2,-3));
		System.out.println(power(-2,3));
		System.out.println(power(3,0));
		System.out.println(power(0,-3));
	}
	public static double power(double base,int exponent) {
		if (equal(base,0.0) && exponent < 0) {
			throw new Error("input error");
		}
		int absExponent = exponent;
		if (exponent < 0) {
			absExponent = 0 - exponent;
		}
		double res = powerCal(base,absExponent);
		if (exponent < 0) {
			res = 1 / res;
		}
		return res;
	}
	public static boolean equal(double numa,double numb) {
		if (numa - numb >= -0.00001 && numa - numb <= 0.00001) {
			return true;
		}
		return false;
	}
	public static double powerCal(double base,int exponent) {
		double res  = 1.0;
		for (int i = 0;i<exponent;i++) {
			res = res * base;
		}
		return res;
	}

}