Give some tests)

Please, give me some test! Or, may be, give some advices about this test.

I can not make tests for which the program gives an incorrect result. Help please

if your program is /tmp/a.out and the input is /tmp/in, you can use the following Python 3 script to plot your output:

from matplotlib.pyplot import *
import subprocess

f = open('/tmp/in')
n = int(f.readline())
p = [[int(i) for i in l.split()] for l in f]
print(p)
out = subprocess.run('/tmp/a.out < /tmp/in', stdout=subprocess.PIPE, shell=True).stdout.decode().strip()
res = [int(s) for s in out.split('\n')[1:]]
print(res)
plot([v[0] for v in p],[v[1] for v in p],'ro')
plot([p[i-1][0] for i in res], [p[i-1][1] for i in res],'b-')
axis('equal'); grid(); show()

My first AC program gets WA on this test:
6
0 0
0 2
1 1
2 2
-1 -1
-2 -2

But I corrected my code :)

I had some trouble passing Test #8.

It turned out that if I used Epsilon = 1e-8 to compare the angles, it worked.

Also, here is a tricky test, with lots of points on the same line:

Input:
10
0 0
1 1
2 2
3 3
4 4
-1 -1
-2 -2
-3 -3
-4 -4
0 1

One possible solution:
10
1
2
3
4
5
10
6
7
8
9

program p1444;
uses math;
const
  maxn=30000;
var
  s:array[1..maxn] of record
                        x,y:longint;
                      end;
  num:array[1..maxn] of longint;
  t,len:array[1..maxn] of double;
  n,m,i,j,k:longint;

procedure readdata;
var
  i,j,k:longint;
begin
  readln(n);
  for i:=1 to n do
    readln(s[i].x,s[i].y);
end;

procedure swap(var a,b:longint); inline;
var temp:longint;
begin
  temp:=a; a:=b; b:=temp;
end;

procedure sp(var a,b:double); inline;
var temp:double;
begin
  temp:=a; a:=b; b:=temp;
end;

procedure qsort(s,b:longint);
var
  i,j:longint;
  tx,lenx:double;
begin
  if s>=b then exit;
  i:=s; j:=b;
  tx:=t[(i+j) shr 1]; lenx:=len[(i+j) shr 1];
  repeat
    while (t[j]>tx)or( (t[j]=tx)and(len[j]>lenx) ) do dec(j);
    while (t[i]<tx)or( (t[i]=tx)and(len[i]<lenx) ) do inc(i);
    if i<=j then
      begin
        swap(num[i],num[j]);
        sp(t[i],t[j]);
        sp(len[i],len[j]);
        inc(i); dec(j);
      end;
  until i>=j;
  qsort(s,j); qsort(i,b);
end;

procedure qsort2(s,b:longint);
var
  i,j:longint;
  tx,lenx:double;
begin
  if s>=b then exit;
  i:=s; j:=b;
  tx:=t[(i+j) shr 1]; lenx:=len[(i+j) shr 1];
  repeat
    while (t[j]<tx)or( (t[j]=tx)and(len[j]>lenx) ) do dec(j);
    while (t[i]>tx)or( (t[i]=tx)and(len[i]<lenx) ) do inc(i);
    if i<=j then
      begin
        swap(num[i],num[j]);
        sp(t[i],t[j]);
        sp(len[i],len[j]);
        inc(i); dec(j);
      end;
  until i>=j;
  qsort2(s,j); qsort2(i,b);
end;

procedure solve;
var
  check:boolean;
  i,j,k:longint;
begin
  for i:=2 to n do
    begin
      dec(s[i].x,s[1].x);
      dec(s[i].y,s[1].y);
    end;
  s[1].x:=0; s[1].y:=0;
  for i:=2 to n do
    len[i]:=sqrt(sqr(s[i].x)+sqr(s[i].y));
  for i:=2 to n do
    begin
      t[i]:=arccos(s[i].x/len[i]);
      if s[i].y<0 then t[i]:=2*pi-t[i];
    end;
  for i:=1 to n do
    num[i]:=i;
  check:=false;
  for i:=2 to n do
    if (abs(t[i]-pi)>1e-8)and(t[i]<pi)and(0<t[i]) then check:=true;
  if check then
    qsort(2,n) else
    begin
      for i:=1 to n do
        if (s[i].x>0)and(t[i]=0) then t[i]:=2*pi;
      qsort2(2,n);
    end;
  writeln(n);
  for i:=1 to n do
    writeln(num[i]);
end;

begin
  readdata;
  solve;
end.

I don't know how could i choose next point.
I have some ideas about it:
1. The solution isn't very complexity(maybe it uses sorting)
2. I think, Elephpotamus always can eat all pumpkins
3. And our path should be spin or smth like it.
Help plz

Hello!

My submit has status "problem locked". What does it mean?

I think, that my program is right... but WA :(
Pls help