nyoj 1029/hdu 3714 Error Curves 三分

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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 0x3fffffffstruct 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));    }}

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