剑指offer十三：数值的整数次方

 

 

 

#include<iostream>
using namespace std;

double PowerWithUnsignedExponent(double base, int exponent);

bool equal(double num1, double num2)
{
	if (abs(num1 - num2) < 0.0000001)
		return true;
	else
		return false;
}

bool InvalidInput = false;
double Power(double base, int exponent)
{
	InvalidInput = false;
	double result;

	//指数小于0时，分母为0，无意义
	if (equal(base, 0) && exponent < 0 )
	{
		InvalidInput = true;
		return 0;
	}
	if (exponent < 0)//指数小于0（要考虑分母为0时，即上面的判断）
		result = 1/PowerWithUnsignedExponent(base, -exponent);
	else//指数大于0
		result = PowerWithUnsignedExponent(base, exponent);
	return InvalidInput, result;
}

//指数大于0
double PowerWithUnsignedExponent(double base, int exponent)
{
	int result = 1;
	for (int i = 0; i < exponent; i++)
		result *= base;
	return result;
}

int main()
{	
	double base;
	int exponent;
	cout << "ple input a base:" << endl;
	cin >> base;
	cout << "pls input a exponent" << endl;
	cin >> exponent;

	double result = Power(base, exponent);
	cout << InvalidInput << endl;

	//double result = EffectPower(base, exponent);
	cout << result << endl;
}

 

double EffectPower(double base, unsigned int exponent)
{
	if (exponent == 0)
		return 1;
	if (exponent == 1)
		return base;
	double result = EffectPower(base, exponent >> 1);
	result *= result;
	if (exponent % 2 == 1)//指数为奇数
		result *= base;
	return result;
}