hdu2899 简单数学+二分+三分

二分思想       了解二分与三分的适用情况

二分代码:

#include<iostream>
#include<cmath>
#include<cstdio>
using namespace std;
const double b=1e-6;
double f(double x)
{
    return 42*pow(x,6)+48*pow(x,5)+21*pow(x,2)+10*x;
}
double F(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 T;
    double x,y,l,r;
    cin>>T;
    while(T--)
    {
        cin>>y;
        if(f(100)<=y)
        {
            printf("%.4lf\n",F(100,y));
        }
        else
        {
            l=0;r=100;
            while(r-l>b)
            {
                if(f((r+l)/2)>y) r=(r+l)/2;
                else l=(r+l)/2;
            }
            printf("%.4lf\n",F(l,y));
        }
    }
    return 0;
}

 

三分代码:

#include<iostream>
#include<cmath>
#include<cstdio>
using namespace std;
const double b=1e-6;
double F(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 T;
    double l,r,lm,rm,y;
    cin>>T;
    while(T--)
    {
        cin>>y;
        l=0;r=100;
        while(r-l>b)
        {
            lm=(2*l+r)/3;
            rm=(l+2*r)/3;
            if(F(lm,y)>F(rm,y)) l=lm;
            else r=rm;
        }
        printf("%.4lf\n",F(l,y));
    }
    return 0;
}