面试题16：数值的整数次方（c++）【剑指offer】

一

class Solution {
public:
    double Power(double base, int exponent) {
        bool flag=false;
        double results=1;
        if(base==0 && exponent<0 ){
            results=0;
            flag=true;
            return results;
        }
        int new_exponent=exponent;
        if(exponent<0) new_exponent=-exponent;
        double tmp=unsignedPower(base,new_exponent);
        if(exponent<0) results=1/tmp;
        else results=tmp;
        return results;
    }
    double unsignedPower(double base,int new_exponent){
        if(new_exponent==0) return 1;
        double results=1;
        for(int i=1;i<=new_exponent;i++){
            results*=base;
        }
        return results;
    }
};

二

class Solution {
public:
    double Power(double base, int exponent) {
        bool flag=false;
        double results=1;
        if(base==0 && exponent<0 ){
            results=0;
            flag=true;
            return results;
        }
        int new_exponent=exponent;
        if(exponent<0) new_exponent=-exponent;
        double tmp=unsignedPower(base,new_exponent);
        if(exponent<0) results=1/tmp;
        else results=tmp;
        return results;
    }
    double unsignedPower(double base,int new_exponent){
        if(new_exponent==0) return 1;
        if(new_exponent==1) return base;
        double results;
        int b=new_exponent/2;
        double tmp2=unsignedPower(base,b);
        results=tmp2*tmp2;
        if(new_exponent%2==1) results*=base;
        return results;
    }
};

三

class Solution {
public:
    double Power(double base, int exponent) {
        bool flag=false;
        double results=1;
        if(base==0 && exponent<0 ){
            results=0;
            flag=true;
            return results;
        }
        int new_exponent=exponent;
        if(exponent<0) new_exponent=-exponent;
        double tmp=unsignedPower(base,new_exponent);
        if(exponent<0) results=1/tmp;
        else results=tmp;
        return results;
    }
    double unsignedPower(double base,int new_exponent){
        if(new_exponent==0) return 1;
        if(new_exponent==1) return base;
        double results=unsignedPower(base,new_exponent>>1);
        results*=results;
        if(new_exponent & 0x1 ==1) results*=base;
        return results;
    }
};