[省选前题目整理][BZOJ 1857][SCOI 2010]传送带(三分套三分)

题目链接

思路

代码

#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <algorithm>
#include <cmath>

#define EPS 1e-4

using namespace std;

double P,Q,R,ax,ay,bx,by,cx,cy,dx,dy;

inline double dist(double x1,double y1,double x2,double y2)
{
return sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
}

inline double calc(double sx,double sy) //在(sx,sy)处离开传送带AB
{
double lowerBoundx=cx,upperBoundx=dx;
double lowerBoundy=cy,upperBoundy=dy;
while(fabs(upperBoundx-lowerBoundx)>EPS||fabs(upperBoundy-lowerBoundy)>EPS)
{
double midx1=lowerBoundx+(upperBoundx-lowerBoundx)/3,midx2=upperBoundx-(upperBoundx-lowerBoundx)/3;
double midy1=lowerBoundy+(upperBoundy-lowerBoundy)/3,midy2=upperBoundy-(upperBoundy-lowerBoundy)/3;
double f1=dist(ax,ay,sx,sy)/P+dist(sx,sy,midx1,midy1)/R+dist(midx1,midy1,dx,dy)/Q;
double f2=dist(ax,ay,sx,sy)/P+dist(sx,sy,midx2,midy2)/R+dist(midx2,midy2,dx,dy)/Q;
if(f1<f2) upperBoundx=midx2,upperBoundy=midy2;
else lowerBoundx=midx1,lowerBoundy=midy1;
}
return dist(ax,ay,sx,sy)/P+dist(sx,sy,lowerBoundx,lowerBoundy)/R+dist(lowerBoundx,lowerBoundy,dx,dy)/Q;
}

int main()
{
scanf("%lf%lf%lf%lf%lf%lf%lf%lf%lf%lf%lf",&ax,&ay,&bx,&by,&cx,&cy,&dx,&dy,&P,&Q,&R);
double lowerBoundx=ax,upperBoundx=bx;
double lowerBoundy=ay,upperBoundy=by;
while(fabs(upperBoundx-lowerBoundx)>EPS||fabs(upperBoundy-lowerBoundy)>EPS)
{
double midx1=lowerBoundx+(upperBoundx-lowerBoundx)/3,midx2=upperBoundx-(upperBoundx-lowerBoundx)/3;
double midy1=lowerBoundy+(upperBoundy-lowerBoundy)/3,midy2=upperBoundy-(upperBoundy-lowerBoundy)/3;
double f1=calc(midx1,midy1),f2=calc(midx2,midy2);
if(f1<f2) upperBoundx=midx2,upperBoundy=midy2;
else lowerBoundx=midx1,lowerBoundy=midy1;
}
printf("%.2lf",calc(lowerBoundx,lowerBoundy));
return 0;
}