【模板】【洛谷 P3382】三分

链接：https://www.luogu.org/problem/show?pid=3382

#include<iostream>#include<cstring>#include<cstdio>#include<algorithm>using namespace std;double l,r;int n;const double eps=1e-7;double a[1000];double f(double x){    double ans=a[1];    for(int i=2;i<=n+1;i++)        ans=ans*x+a[i];    return ans;}int main(){    scanf("%d%lf%lf",&n,&l,&r);    for(int i=1;i<=n+1;i++) scanf("%lf",&a[i]);    double ll=l,rr=r,midx,midy;        while(rr-ll>eps)        {            midx=(2*ll+rr)/3;            midy=(ll+2*rr)/3;            if(f(midx)<f(midy)) ll=midx;            else rr=midy;        }    printf("%.5lf\n",ll);    return 0;}