HDOJ 2899 求极点+二分

#include<iostream>
#include<cmath>
#define Min(a,b) (a<b?a:b)

using namespace std;

/*   F(x) = 6*x^7 + 8*x^6 + 7*x^3 +5*x^2 -y*x
 *   F(x)'= 42x^6 + 48*x^5 + 21*x^2 + 10*x = y
 */

double get_sum(double x){
	return x*x*x*x*x*x*42+x*x*x*x*x*48+x*x*21+x*10;
}

double bin_search(double Y){
	double low=0;
	double high=100;
	double mid;
	while(low<high){
		mid=(low+high)/2;
		//cout<<mid<<endl;
		double tmp=get_sum(mid);
		if( fabs(tmp - Y) < 0.00001 )
			return mid;
		else if(tmp > Y)
		   	high = mid;
		else 
			low = mid;
	}
	return mid;
}

int main(){
	int T;
	cin>>T;
	while(T--){
		double Y;
		cin>>Y;
		double x=bin_search(Y);
		printf("%.4lf\n",6*pow(x,7)+8*pow(x,6)+7*x*x*x+5*x*x-Y*x);
	}
	return 0;
}