Line belt HDU

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原题：HDU- 3400

三分搜索用来找中间最优点，设变量l、r、mid=(l+r)/2、mmid=(mid+r)/2；一步步向最优值逼近，适用于二次函数模型

这个题以找AB的最优点来寻找CD的最优点，用两个三分搜索

#include <iostream>#include <cstdio>#include <algorithm>#include <cmath>using namespace std;double Ax,Ay,Bx,By,Cx,Cy,Dx,Dy;double p,q,r;double f4(double x1,double y1,double x2,double y2) {    return sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));}double f3(double xie,double x1,double y1) {    double x=Cx+(Dx-Cx)*xie;    double y=Cy+(Dy-Cy)*xie;    return f4(x,y,x1,y1)/r+f4(x,y,Dx,Dy)/q;}double f2(double xie) {    double x=Ax+(Bx-Ax)*xie;    double y=Ay+(By-Ay)*xie;    double l=0.0,r=1.0,mid,mmid,t1,t2;    while(r-l>1e-8) {        mid=(r+l)/2;        mmid=(mid+r)/2;        t1=f3(mid,x,y);        t2=f3(mmid,x,y);        if(t1<t2)            r=mmid;        else if(t1>t2)            l=mid;        else break;    }    return t1+f4(x,y,Ax,Ay)/p;}double f1() {    double l=0.0,r=1.0,mid,mmid,t1,t2;    while(r-l>1e-8) {        mid=(r+l)/2;        mmid=(mid+r)/2;        t1=f2(mid);        t2=f2(mmid);        if(t1<t2)            r=mmid;        else if(t1>t2)            l=mid;        else break;    }    return t1;}int main() {    int T;    scanf("%d",&T);    while(T--) {        scanf("%lf %lf %lf %lf",&Ax,&Ay,&Bx,&By);        scanf("%lf %lf %lf %lf",&Cx,&Cy,&Dx,&Dy);        scanf("%lf %lf %lf",&p,&q,&r);        printf("%.2f\n",f1());    }    return 0;}

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