2014
01-26

# Fire-Control System

A new mighty weapon has just been developed, which is so powerful that it can attack a sector of indefinite size, as long as the center of the circle containing the sector is the location of the weapon. We are interested in developing a fire-control system that calculates firing-solutions automatically.
The following example gives an example of a firing solution:
Figure 1

Here the firing region is the sector "ABC" that covers six points: A, B, C, D, E, H. You may further assume that the weapon is always located at point (0, 0), no targets will be on the point (0, 0) and the coordinates of the targets will be distinct.
A firing solution is called effective if and only if it covers a minimum of K points
out of N given points (targets) on the two-dimensional Cartesian plane. Furthermore,since the cost of a particular fire solution is in direct proportion to the size of the area it covers, a firing could be quite costly; thus we are only interested in the optimal firing solution with the minimum cost.

There are multiple test cases in the input file.
Each test case starts with two non-negative integers, N and K
(1 ≤ N ≤ 5000 , K ≤ N ), followed by N lines each containing two integers, X, and Y, describing the distinct location of one target. It is guaranteed that the absolute value of any integer does not exceed 1000.
Two successive test cases are separated by a blank line. A case with N = 0 and K = 0 indicates the end of the input file, and should not be processed by your program.

There are multiple test cases in the input file.
Each test case starts with two non-negative integers, N and K
(1 ≤ N ≤ 5000 , K ≤ N ), followed by N lines each containing two integers, X, and Y, describing the distinct location of one target. It is guaranteed that the absolute value of any integer does not exceed 1000.
Two successive test cases are separated by a blank line. A case with N = 0 and K = 0 indicates the end of the input file, and should not be processed by your program.

3 1
0 1
1 0
-5 -6
3 2
0 2
2 0
-5 -6
0 0

Case #1: 0.00
Case #2: 3.14

#include <iostream>
#include <stdio.h>
#include <queue>
#include <algorithm>
#include <math.h>
#include <string.h>
using namespace std;
#define N 100100
#define PI (2*asin(1.0))

struct node
{
int x,y;
double r;//表示半径
double du;//用来表示角度
}g[N];

int n,k;
double g1[N];

int cmp(node t,node t1)
{
return t.du<t1.du;
}

double que[2*N];

double mabs(double x)
{
if(x<0) return -x;
return x;
}

int main()
{
//freopen("//home//ismdeep//xianchang1//in","r",stdin);
int tt=1;
double pi=PI;
while(scanf("%d%d",&n,&k)&&(n+k))
{

for(int i=1;i<=n;i++)
{
scanf("%d%d",&g[i].x,&g[i].y);
g[i].r=sqrt((double)g[i].x*g[i].x+g[i].y*g[i].y);
g1[i]=g[i].r;

double tmp;

if(mabs(g[i].x-0)<1e-8)
{
if(g[i].y>0) tmp=90.0;
else tmp=270.0;
}
else
{
tmp=((double)g[i].y/(double)g[i].x); //将这个点的斜率求出来
if(mabs(g[i].y-0)<1e-8)
{
if(g[i].x>0) tmp=0.0;
else tmp=180.0;
}
else
{
tmp=atan(tmp);//求出角度
tmp=(180.0/PI)*tmp;
if(g[i].y*g[i].x > 0&&g[i].y<0)
tmp+=180.0;
if(g[i].y*g[i].x<0)
{
tmp*=-1;
if(g[i].x<0)
tmp=180.0-tmp;
else
{
tmp=360-tmp;
}
}

}
}
g[i].du=tmp;
}
// 角度求好了
if(k==0)
{
printf("Case #%d: 0.00\n",tt++);
continue;
}
//sort(g1+1,g1+n+1); //半径从小到大来搞一搞啊
sort(g+1,g+1+n,cmp);

double mi=1999999999;

for(int ii=1;ii<=n;ii++)
{
double key=g1[ii]; //表示固定的半径
int flag=0;

for(int i=1;i<=n;i++)//提前
{
if(g[i].r <= key+1e-6)
{
que[flag++]=g[i].du;
}
}

for(int i=0;i<flag;i++)
{
que[flag+i] = que[i]+360.0;
}

if(flag<k) continue;

for(int i=0;i<flag;i++)
{
double tmp=que[i];
int tt=i+k-1;
double tmp1=que[tt];
tmp=tmp1-tmp;

tmp=(tmp/(360.0))*PI*key*key;

mi=min(tmp,mi);
}
}

printf("Case #%d: ",tt++);

printf("%.2lf\n",mi);
}
return 0;
}

1. 5.1处，反了；“上一个操作符的优先级比操作符ch的优先级大，或栈是空的就入栈。”如代码所述，应为“上一个操作符的优先级比操作符ch的优先级小，或栈是空的就入栈。”

2. 这道题目虽然简单，但是小编做的很到位，应该会给很多人启发吧！对于面试当中不给开辟额外空间的问题不是绝对的，实际上至少是允许少数变量存在的。之前遇到相似的问题也是恍然大悟，今天看到小编这篇文章相见恨晚。