Error Curves HDU - 3714 三分

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#include <iostream>
#include <cmath>
#include <cstdio>
#include <algorithm>

using namespace std;

int a[11111],b[11111],c[11111];

const double eps=1e-9;

int sgn(double x)
{
    if(fabs(x)<eps)
        return 0;
    if(x<0)
        return -1;
    else
        return 1;
}

int m;
double f(double x)
{
    double ans=-1e18;
    for(int i=0;i<m;i++)
    {
        ans=max(ans,a[i]*x*x+b[i]*x+c[i]);
    }
    return ans;
}

double three_search(double l,double r)
{
    while(sgn(r-l)>0)
    {
        double lmid=l+(r-l)/3;
        double rmid=r-(r-l)/3;
        if(f(lmid)<=f(rmid))
            r=rmid;
        else
            l=lmid;
    }
    return f(l);
}
int main()
{
    int n;
    scanf("%d",&n);
    while(n--)
    {
        scanf("%d",&m);
        for(int i=0;i<m;i++)
        {
            scanf("%d %d %d",&a[i],&b[i],&c[i]);
        }
        double l=0.0;
        double r=1000.0;
        double ans=three_search(l,r);
        printf("%.4lf\n",ans);
    }
    return 0;
}