HDUOJ---The Moving Points

The Moving Points

Time Limit: 6000/3000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others) Total Submission(s): 612    Accepted Submission(s): 250

Problem Description

There are N points in total. Every point moves in certain direction and certain speed. We want to know at what time that the largest distance between any two points would be minimum. And also, we require you to calculate that minimum distance. We guarantee that no two points will move in exactly same speed and direction.

 

Input

The rst line has a number T (T <= 10) , indicating the number of test cases. For each test case, first line has a single number N (N <= 300), which is the number of points. For next N lines, each come with four integers X_i, Y_i, VX_i and VY_i (-10⁶ <= X_i, Y_i <= 10⁶, -10² <= VX_i , VY_i <= 10²), (X_i, Y_i) is the position of the i^th point, and (VX_i , VY_i) is its speed with direction. That is to say, after 1 second, this point will move to (X_i + VX_i , Y_i + VY_i).

 

Output

For test case X, output "Case #X: " first, then output two numbers, rounded to 0.01, as the answer of time and distance.

 

Sample Input

2 2 0 0 1 0 2 0 -1 0 2 0 0 1 0 2 1 -1 0

 

Sample Output

Case #1: 1.00 0.00 Case #2: 1.00 1.00

 

Source

2013 ACM/ICPC Asia Regional Online —— Warmup2

 

Recommend

zhuyuanchen520

三分思路：

单调性查找就好....对时间

代码：

#include<iostream>
#include<vector>
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<cmath>
#define MAX 1e9
#define exp 1e-6
using namespace std;
   //设置结构体
typedef struct 
{
    int x,y;
    int px,py;
}point;

   //计算任意时间两点的距离
double das(point a,point b,double t )
{
    return  sqrt(pow(((a.x+a.px*t)-(b.x+b.px*t)),2)+pow(((a.y+a.py*t)-(b.y+b.py*t)),2)); 
}
   //判断两个数最大值....
double max( double a,double b)
{
    return a>b?a:b; 
}
point po[305];
 int main()
 { 
    int n,i,j,cnt=1,t;
    double ll,rr,ml,mr,ans1,ans2;
    scanf("%d",&t);
    while(t--)
    {
      scanf("%d",&n);
      for( i=1 ; i<=n ; i++ )
      {
       scanf("%d%d%d%d",&po[i].x,&po[i].y,&po[i].px,&po[i].py);
       //cin>>po[i].x>>po[i].y>>po[i].px>>po[i].py;
      }
     //没有其他的办法，除了遍历之外
      ll=0.0,rr=MAX;
     while(rr-ll>exp)
     {
        ans1=ans2=0.0;
        //ml=(ll+rr)/2.0;   //慢很多
         //mr=(ml+rr)/2.0;
        ml=(ll*2+rr)/3.0;       // r/3.0  较快
        mr=(ll+rr*2)/3.0;       // 2*r/3.0
       for( i=1 ; i<n ; i++ )  
       {
         for( j=i+1 ; j<=n ;j++ )
         {
             ans1=max(ans1,das(po[i],po[j],ml));  //对左边
             ans2=max(ans2,das(po[i],po[j],mr));  //对右边
         }
       }
        if( ans1<ans2 ) 
              rr=mr;
        else
             ll=ml;
     }
       //得到时间ll or rr 都可以
      ans1=0.0;
      for(i=1 ; i<n ; i++ )
       {
         for(j=1+i ; j<=n ;j++)
         {
             ans1=max(ans1,das(po[i],po[j],ll));  //对左边ll/rr
         }
     }
     printf("Case #%d: %.2lf %.2lf
",cnt++,ll,ans1);
    }
    return 0;
 }