nyoj 1029/hdu 3714 Error Curves 三分

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=3714

懂了三分思想和F(x)函数的单调性质，这题也就是水题了

#include "stdio.h"  //最后得到的F(x)函数要么是单调的，要么是先减后增的，有了这个性质，就可以三分了~
#include "string.h"
 
#define N 10005
#define eps 1e-9
#define INF 0x3fffffff
 
struct node
{
    int a;
    int b;
    int c;
}q[N];
 
int n;
 
double S(double x)
{
    double sx;
    double maxt = -INF;
    for(int i=0; i<n; ++i)
    {
        sx = q[i].a*x*x+q[i].b*x+q[i].c;
        if(sx>maxt)
            maxt = sx;
    }
    return maxt;
}
 
int main()
{
    int i,T;
    double ans_mid,ans_mid_mid;
    double left,right,mid,mid_mid;
    scanf("%d",&T);
    while(T--)
    {
        scanf("%d",&n);
        for(i=0; i<n; ++i)
            scanf("%d %d %d",&q[i].a,&q[i].b,&q[i].c);
        left = 0;
        right = 1000;
        while(right-left>eps)
        {
            mid = (right+left)/2;
            ans_mid = S(mid);
            mid_mid = (mid+right)/2;
            ans_mid_mid = S(mid_mid);
            if(ans_mid>ans_mid_mid)
                left = mid;
            else
                right=  mid_mid;
        }
        printf("%.4lf\n",S(right));
    }
}