[BZOJ1610][Usaco2008 Feb]Line连线游戏

传送门

http://www.lydsy.com/JudgeOnline/problem.php?id=1610

题目大意

给n个点,有多少种斜率

题解

直接求斜率,然后排序判断即可,注意不存在斜率的情况

var
 z:array[0..40005]of double;
 x,y:array[0..205]of longint;
 i,j,k:longint;
 n,len,ans:longint;
procedure sort(l,r:longint);
var i,j:longint; a,b:real;
begin
 i:=l; j:=r; a:=z[(l+r) div 2];
 repeat
  while z[i]<a do inc(i);
  while a<z[j] do dec(j);
  if not(i>j) then
   begin
    b:=z[i]; z[i]:=z[j]; z[j]:=b;
    inc(i); dec(j);
   end;
 until i>j;
 if l<j then sort(l,j);
 if i<r then sort(i,r);
end;

begin
 readln(n); len:=0;
 for i:=1 to n do
  readln(x[i],y[i]);
 for i:=1 to n do
  for j:=i+1 to n do
   begin
    inc(len);
    if x[i]=x[j]
    then z[len]:=maxlongint
    else z[len]:=(y[i]-y[j])/(x[i]-x[j]);
   end;
 sort(1,len); {z[i]}
 z[0]:=-2; ans:=0;
 for i:=1 to len do
  if z[i]<>z[i-1]
  then inc(ans);
 writeln(ans);
end.