HDU 2899 （二分&三分_H题）解题报告

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=2899

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题意：  F(x) = 6 * x^7+8*x^6+7*x^3+5*x^2-y*x (0 <= x <=100)求最小值。

思路：求极值，三分法。

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-8;
double Y;

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

double bsearch(){
    double left =0;
    double right =100;
    double midr=0;
    double midl=0;
    while(right-left>=eps){
        midl=(left+right)*0.5;
        midr=(midl+right)*0.5;
        double cmidl=cal(midl);
        double cmidr=cal(midr);
        if(cmidl<cmidr){
            right =midr;
        }else{
            left =midl;
        }
    }
    return left;
}

int main(void){
    int T =0;
    scanf("%d",&T);
    for(int i=0;i<T;i++){
        scanf("%lf",&Y);
        printf("%.4lf\n",cal(bsearch()));
    }
    

    return 0;

}