2013湘大ACM多省比赛-hurry up

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题目连接

题意：没什么可谈的，就是一个几何+三分查找题，列出关系式，在x1到x2之间找出最小值，该函数是一个凸函数，利用三分查找，是最合适不过了。

要注意精度。

代码：

#include<stdio.h>#include<math.h>#define eps 1e-8double v1,v2,low,high;int sign(double x){return x < -eps ? -1 : x > eps;}double count(double a,double b,double c,double d){return sqrt((a-c)*(a-c)+(b-d)*(b-d));}double search(double x1,double y1,double x2,double y2 ){double mid1,mid2,min;while(sign(high - low) >=0)      //eps代表精度 {mid1=(low+high)/2;mid2=(mid1+high)/2;double L=count(x1,y1,mid1,0)/v1+count(x2,y2,mid1,0)/v2;double r=count(x1,y1,mid2,0)/v1+count(x2,y2,mid2,0)/v2;if(sign(L-r) < 0){ high=mid2-eps; min=L;}else { low=mid1+eps; min=r;}}return min;}int main(){int n;double x1,x2,y1,y2;scanf("%d",&n);while(n--){scanf("%lf%lf%lf%lf%lf%lf",&x1,&y1,&x2,&y2,&v1,&v2);double w=count(x1,y1,x2,y2)/v1;low=x1<x2?x1:x2;high=x2>x1?x2:x1;    double t=search(x1,y1,x2,y2);if(w<t)    printf("%.2lf\n",w);else    printf("%.2lf\n",t);}return 0;}/*101 1 2 2 1 70 3 4 0 1 20 3 6 0 2 4*/