【模板】三分法（板子）

题目链接https://www.luogu.com.cn/problem/P3382

代码

#include<iostream>
#include<string>
#include<map>
//#include<unordered_map>
#include<queue>
#include<cstdio>
#include<vector>
#include<cstring>
#include<algorithm>
#include<iomanip>
#include<cmath>
#include<fstream>
#define X first
#define Y second
#define best 131 
#define INF 0x3f3f3f3f
#define P pair<int,int>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
const double eps=1e-7;
const double pai=acos(-1.0);
const int N=2e4+10;
const int maxn=110;
const int mod=1e9+7;
//const int d[4][2]={0,1,1,0,-1,0,0,-1};
int n;
double l,r;
double a[15];
double f(double x)
{
	double res=0;
	for(int i=0;i<=n;i++)
	{
		res=res*x+a[i];
	}
	return res;
}
int main()
{
//	ios::sync_with_stdio(false);
    //memset(mp,-1,sizeof(mp));
        scanf("%d%lf%lf",&n,&l,&r);
	for(int i=0;i<=n;i++) scanf("%lf",&a[i]);
	while(r-l>eps)
	{
		double k=(r-l)/3.0;
		double mid1=l+k,mid2=r-k;
		if(f(mid1)>f(mid2)) r=mid2;
		else l=mid1;
	}
	printf("%.5f\n",l);
	return 0;
}