链接Miku

三分模板

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
using namespace std;
int n;
double l,r;
double xi[20];
double xiu=0.000001;
double check(double x){
    double ans=0.0;
    for(int i=1;i<=n;++i){
        double anss=1.0;
        for(int j=1;j<=i;++j)
        anss*=x;
        ans=ans+anss*xi[n-i+1];
    }
    return ans;
}
int main(){
    scanf("%d%lf%lf",&n,&l,&r);
    for(int i=1;i<=n;++i){
        scanf("%lf",&xi[i]);
    }
    while(l+xiu<r){
        double ll=l+(r-l)*0.3;
        double rr=l+(r-l)*0.7;
        if(check(ll)<check(rr))
            l=ll;
            else
            r=rr;
    }
    printf("%.5lf",l);
    return 0;
}