HDU 5105

题意略。

思路：

考察导数和分类讨论的思想，因为在做题时少讨论一种情况，所以wa了。

#include<bits/stdc++.h>
using namespace std;

double a,b,c,d,L,R;

double func(double x){
    return fabs(a * x * x * x + b * x * x + c * x + d);
}

int main(){
    while(scanf("%lf%lf%lf%lf%lf%lf",&a,&b,&c,&d,&L,&R) == 6){
        double ans = 0;
        double ansl = func(L),ansr = func(R);
        if(a != 0){
            double d = b * b - 3 * a * c;
            if(d <= 0){
                ans = max(ansl,ansr);
            }
            else{
                double x1 = (-1 * b - sqrt(d)) / (3 * a);
                double x2 = (-1 * b + sqrt(d)) / (3 * a);
                double ans1 = func(x1),ans2 = func(x2);
                if(L <= x1 && x2 <= R){
                    ans = max(max(ans1,ans2),max(ansl,ansr));
                }else if(R <= x1 || L >= x2){
                    ans = max(ansl,ansr);
                }else if(L <= x1 && x1 <= R && R <= x2){
                    ans = max(ans1,max(ansl,ansr));
                }else if(x1 <= L && R <= x2){
                    ans = max(ansl,ansr);
                }else if(x1 <= L && L <= x2 && x2 <= R){
                    ans = max(ans2,max(ansl,ansr));
                }
            }
        }else if(b != 0){
            double x0 = -c / (2 * b);
            if(R <= x0){
                ans = max(ansl,ansr);
            }else if(L <= x0 && x0 <= R){
                ans = max(func(x0),max(ansl,ansr));
            }else{
                ans = max(ansl,ansr);
            }
        }else if(c != 0){
            ans = max(ansl,ansr);
        }else{
            ans = fabs(d);
        }
        printf("%.2lf
",ans);
    }
    return 0;
}