HDU2899 Strange fuction（三分模板）

HDU2899 Strange fuction

Problem Description

Now, here is a fuction:
F(x) = 6 * x^7+8*x6+7x^3+5*x2-yx (0 <= x <=100)
Can you find the minimum value when x is between 0 and 100.

Input

The first line of the input contains an integer T(1<=T<=100) which means the number of test cases. Then T lines follow, each line has only one real numbers Y.(0 < Y <1e10)

Output

Just the minimum value (accurate up to 4 decimal places),when x is between 0 and 100.

Sample Input

2
100
200

Sample Output

-74.4291
-178.8534

题解

题意

找函数最小值

题解

三分标准例题，整理模板

代码

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<iostream>
#include<string>
#include<vector>
#include<stack>
#include<bitset>
#include<cstdlib>
#include<cmath>
#include<set>
#include<list>
#include<deque>
#include<map>
#include<queue>
using namespace std;
typedef long long ll;
const double PI = acos(-1.0);
const double eps = 1e-6;
const int INF = 0x3f3f3f3f;

double y = 0;

double cal (double x){
	return 6 * pow(x,7)+8*pow(x,6)+7*pow(x,3)+5*pow(x,2)-y*x;
}



double tri(){
	double midl,midr;
	double left=0;
	double right=100;
	while(left+eps<right){
		midl = (left+right)/2;
		midr = (midl+right)/2;
		double cmidl = cal(midl);
		double cmidr = cal(midr);
		if(cmidl<cmidr){
			right = midr;
		}else{
			left = midl;
		}
	}
	return left;
}

int main(){
	int T = 0;
	while(~scanf("%d",&T)){
		for(int i=0;i<T;i++){
			scanf("%lf",&y);
			double ans = tri();
			printf("%.4f\n",cal(ans));
		}
	}
	return 0;
}