剑指offer 12：数值的整数次方

public class Solution {
    public double Power(double base, int exponent) {
        boolean isNegtive = false;
        if(exponent == 0)
            return 1;
        if(exponent == 1)
            return base;
        if(exponent < 0){
            isNegtive = true;
            exponent *= -1;
        }
        double pow = Power(base*base, exponent>>1);
        if((exponent & 0x1)== 1){
            pow *= base;
        }
        return isNegtive ? 1/pow : pow;
  }
}