16 数值的整数次方

牛客

当 n 为偶数时，a^n = a^(n/2) a^(n/2)， n 为奇数时 a^n = a((n-1)/2) a((n-1)/2) * a

时间复杂度 log(n)

public class Solution {
    public double Power(double base, int exponent) {
        if(exponent==0) return 1;

        if(exponent<0) return 1.0/powerCore(base, -exponent);
        return powerCore(base, exponent);
    }
    
    private double powerCore(double base, int exponent){
        
        if(exponent==1) return base;
        if((exponent & 0x1) ==1){
            return Power(base,(exponent-1)>>1) * Power(base,(exponent-1)>>1) * base;
        } else {
            return Power(base, exponent>>1) * Power(base, exponent>>1);
        }
    }
}