【模板】三分法

 1 #include<iostream> 
 2 #include<cstring>
 3 #include<cstdlib>
 4 #include<cstdio>
 5 #include<cmath> 
 6 #include<algorithm> 
 7 using namespace std;
 8 const int maxn=15, inf=1e9;
 9 int n;
10 double l,r,a[maxn];
11 double f(double x){
12     double ans=0, now=1;
13     for(int i=n+1;i;i--) ans+=now*a[i], now*=x;
14     return ans;
15 }
16 int main(){
17     scanf("%d%lf%lf",&n,&l,&r);
18     for(int i=1;i<=n+1;i++) scanf("%lf",&a[i]);
19     while(r-l>1e-6){
20         double mid1=l+(r-l)/3, mid2=l+(r-l)/3*2;
21         if(f(mid1)>f(mid2)) r=mid2;
22         else l=mid1;
23     }
24     printf("%.5lf",l);
25 }