hdu 2899 Strange fuction （三分）

E - Strange fuction

Time Limit:1000MS     Memory Limit:32768KB     64bit IO Format:%I64d & %I64u

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Description

Now, here is a fuction: 
  F(x) = 6 * x^7+8*x^6+7*x^3+5*x^2-y*x (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

 

感觉一开始完全被唬到了 听完凯神说的才知道三分其实和二分没什么本质差别

#include<cstdio>

#include<iostream>

#include<algorithm>

using namespace std;//F(x) = 6 * x^7+8*x^6+7*x^3+5*x^2-y*x (0 <= x <=100)

double pow(double x,int n)

{

    double ans=1.0;

    for(int i=1;i<=n;i++)

    {

        ans*=x;

    }

    return ans;

}

double fun(double x,double y)

{

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

}

int main()

{

    int n;

    double x,y;

    double l,r;

    double midl,midr;

    cin>>n;

    while(n--)

    {

        cin>>y;

        l=0.0;r=100.0;

        while(r-l>=0.0000001)// 这里必须足够小 否则误差较大

        {

            midl=l+(r-l)/3;

            midr=l+2*(r-l)/3;



            if(fun(midl,y)<fun(midr,y)) r=midr;

            else l=midl;

        }

        printf("%.4lf\n",min(fun(l,y),fun(r,y)));

    }

    return 0;

}