三分搜索

#include <iostream>
#include <string.h>
#include <stdio.h>
#include <math.h>
#include <algorithm>
using namespace std;

const double eps=1e-5;
const int MAX=50010;

double p[MAX],w[MAX];
int n;

double equ(double x)
{
double ans=0;
for(int i=0;i<n;i++)
{
double S=fabs(p[i]-x);
ans+=w[i]*S*S*S;
}
return ans;
}

double ternarySearch(double l,double r)
{
while(r-l>eps)
{
double ll=(2*l+r)/3;
double rr=(l+2*r)/3;
double ans1=equ(ll);
double ans2=equ(rr);
if(ans1>ans2)
l=ll;
else
r=rr;
}
return l;
}

int main()
{
int T,i;
scanf("%d",&T);
for(int t=1;t<=T;t++)
{
scanf("%d",&n);
for(i=0;i<n;i++)
scanf("%lf%lf",&p[i],&w[i]);
double l=p[0],r=p[n-1];
double tmp=ternarySearch(l,r);
printf("Case #%d: %.0lf\n",t,equ(tmp));
}
return 0;
}