剑指offer——面试题16：数值的整数次方

// 面试题16：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。

#include <iostream>
#include <cmath>

bool g_InvalidInput = false;
bool equal(double num1, double num2);
double PowerWithUnsignedExponent(double base, unsigned int exponent);

double Power(double base, int exponent)
{
    g_InvalidInput = false;

    if (equal(base, 0.0) && exponent < 0)
    {
        g_InvalidInput = true;
        return 0.0;
    }

    unsigned int absExponent = (unsigned int) (exponent);
    if (exponent < 0)
        absExponent = (unsigned int) (-exponent);

    double result = PowerWithUnsignedExponent(base, absExponent);
    if (exponent < 0)
        result = 1.0 / result;

    return result;
}

/*
double PowerWithUnsignedExponent(double base, unsigned int exponent)
{
    double result = 1.0;
    
    for (int i = 1; i <= exponent; ++i)
        result *= base;
    return result;
}
*/

double PowerWithUnsignedExponent(double base, unsigned int exponent)
{
    if (exponent == 0)
        return 1;
    if (exponent == 1)
        return base;

    double result = PowerWithUnsignedExponent(base, exponent >> 1);
    result *= result;
    if ((exponent & 0x1) == 1)
        result *= base;

    return result;
}

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

// ====================测试代码====================
void Test(const char* testName, double base, int exponent, double expectedResult, bool expectedFlag)
{
    double result = Power(base, exponent);
    if (equal(result, expectedResult) && g_InvalidInput == expectedFlag)
        std::cout << testName << " passed" << std::endl;
    else
        std::cout << testName << " FAILED" << std::endl;
}

int main(int argc, char* argv[])
{
    // 底数、指数都为正数
    Test("Test1", 2, 3, 8, false);

    // 底数为负数、指数为正数
    Test("Test2", -2, 3, -8, false);

    // 指数为负数
    Test("Test3", 2, -3, 0.125, false);

    // 指数为0
    Test("Test4", 2, 0, 1, false);

    // 底数、指数都为0
    Test("Test5", 0, 0, 1, false);

    // 底数为0、指数为正数
    Test("Test6", 0, 4, 0, false);

    // 底数为0、指数为负数
    Test("Test7", 0, -4, 0, true);

    return 0;
}

 本人答案：

#include"iostream"
#include"stdio.h"
#include"stdexcept"
using namespace std;

bool errorFlag=false;

double GetPower(double base,int exponent)
{
    if(exponent==0)
        return 1.0;
    if(exponent==1)
        return base;

    double result=GetPower(base,exponent>>1);
    result*=result;
    if(exponent&1)
        result*=base;
    return result;
}

bool Equal(double num1,double num2)
{
    if((num1-num2)>-0.000001&&(num1-num2)<0.000001)
        return true;
    return false;
}

double Power(double base,int exponent)
{
    errorFlag=false;
    double result=0;
  //  cout<<exponent<<endl;
    if(Equal(base,0)&&exponent<0)
    {
        errorFlag=true;
        return 0;
    }
    if(exponent<0)
    {
        result=1.0/GetPower(base,-exponent);
    }
    else
    {
        result=GetPower(base,exponent);
    }
    return result;
}

void Test(char *testName,double base,int exponent,double expectResult,bool expectFlag)
{
    //注意这里需要后判断flag，不然前面函数没执行，errorFlag值不会得到更新
    if(Equal(Power(base,exponent),expectResult)&&errorFlag==expectFlag)
    {
        cout<<testName<<":passed."<<endl;
    }
    else
    {
        cout<<testName<<":failed."<<endl;
    }
}

int main()
{
    Test("Test1",-2,-2,0.25,false);
    Test("Test2",-2,3,-8,false);
    Test("Test3",-2,0,1,false);
    Test("Test4",0,-2,0,true);
    Test("Test5",0,0,1,false);
    Test("Test6",0,2,0,false);
    Test("Test7",2,3,8,false);
    Test("Test8",2,-1,0.5,false);
    Test("Test9",2,0,1,false);
    return 0;
}