HDOJ 2199 二分

函数 8*x^4 + 7*x^3 + 2*x^2 + 3*x + 6 == Y 在X在[0,100]递增，直接二分求解

#include<iostream>
#include<cmath>
using namespace std;

/*   
 *   8*x^4 + 7*x^3 + 2*x^2 + 3*x + 6 == Y
 *   32*x^3 + 21*x^2 + 4*x
 */

double get_sum(double x){
	return x*x*x*x*8+x*x*x*7+x*x*2+x*3+6;
}

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;
		if( Y<6 || Y>807020306 )
			cout<<"No solution!"<<endl;
		else {
			double ans=bin_search(Y);
			printf("%.4lf\n",ans);
		}
	}
	return 0;
}