剑指offer——数值的整数次方

public class PowerSolution {
 public static double Power(double base, int exponent) {
      //当底数为0，指数小于0，则为非法情况。
     if (equal(base,0.0)&&exponent<0) {
        return 0.0f;
    }
     //当指数小于0的时候即求该数的倒数再乘方
       if (exponent<0) {
           int absExponent = -exponent;
           double result = PowerWithNonNegative(base, absExponent);
           result = 1.0/result;

           return result;
    }else {
        return PowerWithNonNegative(base, exponent);
    }
  }

  //自定义方法来判断两个double的数是不是相等，因为有误差所以在范围内都认为相等
 public static boolean equal(double a, double b){
     if (((a-b)>-0.00000001)&&((a-b)<0.00000001)) {
        return true;
    }else {
        return false;
    }

 }

 public static double PowerWithNonNegative(double base, int exponent){
        if(exponent==0){
            return 1;
        }

        if(exponent==1){
            return base;
        }

       double result = PowerWithNonNegative(base,exponent>>1);
       result*=result;

        //如果是奇数次方的情况，最终除2余1要与base相乘
        if((exponent&0x1)==1){
            result *=base;
        }
        return result;
 }
 }