2017 CCPC 秦皇岛 & ZOJ 3993 - Safest Buildings （概率+规律）

Safest Buildings
Time Limit: 1 Second      Memory Limit: 65536 KB

PUBG is a multiplayer online battle royale video game. In the game, up to one hundred players parachute onto an island and scavenge for weapons and equipment to kill others while avoiding
getting killed themselves. BaoBao is a big fan of the game, but this time he is having some trouble selecting the safest building.
There are  buildings
scattering on the island in the game, and we consider these buildings as points on a two-dimensional plane. At the beginning of each round, a circular safe area whose center is located at (0, 0) with radius  will
be spawned on the island. After some time, the safe area will shrink down towards a random circle with radius  ().
The whole new safe area is e
4000
ntirely contained in the original safe area (may be tangent to the original safe area), and the center of the new safe area is uniformly chosen within the original safe area.
The buildings covered by the new safe area is called the safe buildings. Given the radius of the safe areas and the positions of the buildings, BaoBao wants to find all the buildings
with the largest probability to become safe buildings.

Input

There are multiple test cases. The first line of input contains an integer ,
indicating the number of test cases. For each test case:
The first line contains three integers  (),  and  (),
indicating the number of buildings and the radius of two safe circles.
The following  lines
each contains 2 integers  and  (),
indicating the coordinate of the buildings. Here we assume that the center of the original safe circle is located at ,
and all the buildings are inside the original circle.
It's guaranteed that the sum of  over
all test cases will not exceed 5000.

Output

For each test case output two lines.
The first line contains an integer ,
indicating the number of buildings with the highest probability to become safe buildings.
The second line contains  integers
separated by a space in ascending order, indicating the indices of safest buildings.
Please, DO NOT output extra spaces at the end of each line.

Sample Input

2
3 10 5
3 4
3 5
3 6
3 10 4
-7 -6
4 5
5 4

Sample Output

1
1
2
2 3

这题只要找规律就行。

在这个大圆里面，最外圈的概率逐渐减小，往里的一个圆环概率相等，最里的小圆概率为1.（如果存在）至于每个的范围是多少可以自己推到（猜测）

按照要求输出。

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

using namespace std;
const int maxn = 100+10;
struct node
{
int s;
int flag;
} a[maxn];
int dis(int x,int y)
{
return x*x+y*y;
}
bool cmd(node a,node b)
{
if(a.s!=b.s)
return a.s<b.s;
return a.flag<b.flag;

}
int main()
{
int T;
scanf("%d",&T);
while(T--)
{
int n,R,r;
scanf("%d %d %d",&n,&R,&r);
for(int i=1; i<=n; i++)
{
int x,y;
scanf("%d %d",&x,&y);
a[i].flag=i;
a[i].s=dis(x,y);
}
sort(a+1,a+1+n,cmd);
int cnt=0;
int ans[maxn];

if(R-2*r<=0)
{
int d=2*r-R;
for(int i=1; i<=n; i++)
{
if(a[i].s<=d*d)
{
cnt++;
ans[cnt]=a[i].flag;
}
}
}
if(cnt!=0)
{
printf("%d\n",cnt);
sort(ans+1,ans+1+cnt);
for(int i=1; i<=cnt; i++)
{
printf("%d%c",ans[i],i==cnt?'\n':' ');
}
continue;
}

for(int i=1;i<=n;i++){

if(a[i].s<=(R-2*r)*(R-2*r)){
ans[++cnt]=a[i].flag;
}else{
break;
}
}
if(cnt!=0){
printf("%d\n",cnt);
sort(ans+1,ans+1+cnt);
for(int i=1; i<=cnt; i++)
{
printf("%d%c",ans[i],i==cnt?'\n':' ');
}
continue;
}

int now=a[1].s;
cnt++;
for(int i=2; i<=n; i++)
{
if(a[i].s==now)
{
cnt++;
}
else
{
break;
}
}
printf("%d\n",cnt);
for(int i=1; i<=cnt; i++)
{
ans[i]=a[i].flag;
}
sort(ans+1,ans+1+cnt);
for(int i=1; i<=cnt; i++)
{
printf("%d%c",ans[i],i==cnt?'\n':' ');
}
}

return 0;
}