{HDU}{4082}{Hou Yi's secret}{几何}

11年北京赛区的B题，数据量很小暴力搜索的计算几何，但是有很多小地方需要注意，WA了N次：

• 注意对点判重，否则乎会生成很多一样的三角形

• 三个点在同一条直线上的情况

• 判断相似性的时候不需要判断角度，只需要对边进行比例判定即可
  
  

#include <iostream>
#include <string>
#include <cstring>
#include <cstdio>
#include <algorithm>
#include <memory>
#include <cmath>
#include <bitset>
#include <queue>
#include <vector>
#include <stack>
using namespace std;

const int MAXN = 20;

#define CLR(x,y) memset(x,y,sizeof(x))
#define MIN(m,v) (m)<(v)?(m):(v)
#define MAX(m,v) (m)>(v)?(m):(v)
#define ABS(x) ((x)>0?(x):-(x))
#define rep(i,x,y) for(i=x;i<y;++i)

typedef struct{
	int a,b,c;
}Node;
Node node[100000];
int N,tt,ans;
int a[MAXN][2];
bool _check(int a1,int b1,
		int a2,int b2,
		int a3,int b3)
{
	int x1 = a1-a2;
	int y1 = b1-b2;
	int x2 = a2-a3;
	int y2 = b2-b3;
	if ( x1*y2 - x2*y1 == 0)
		return false;
	return true;
}
int _dist(const int & a1, const int& b1,
		const int &a2, const int& b2)
{
	return (a1-a2)*(a1-a2)+(b1-b2)*(b1-b2);
}
bool _sim(const int& i, const int& j)
{
	if( node[i].a*node[j].b - node[j].a*node[i].b != 0)
		return false;
	if( node[i].a*node[j].c - node[j].a*node[i].c != 0)
		return false;
	return true;
}
int work()
{
	int i,j,tmp,k;
	int x,y;
	int v[300][300];
	CLR(v,0);
	int n = 0;
	rep(i,0,N){
		scanf("%d%d",&x,&y);
		if( v[x+150][y+150] )
			continue;
		v[x+150][y+150] = true;
		a[n][0] = x;
		a[n][1] = y;
		++n;
	}
	int cnt = 0;
	int e[3];
	rep(i,0,n)
		rep(j,i+1,n)
			rep(k,j+1,n){
				if(!_check(a[i][0],a[i][1],
							a[j][0],a[j][1],
							a[k][0],a[k][1]))
					continue;

				e[0] = _dist(a[i][0],a[i][1],a[j][0],a[j][1]);
				e[1] = _dist(a[i][0],a[i][1],a[k][0],a[k][1]);
				e[2] = _dist(a[k][0],a[k][1],a[j][0],a[j][1]);
				sort(e,e+3);
				node[cnt].a = e[0];
				node[cnt].b = e[1];
				node[cnt].c = e[2];
				++cnt;
			}
	int mmax;
	mmax = 0;
	if( cnt > 1 ){
		tmp = 1;
		rep(i,0,cnt){
			tmp = 1;
			rep(j,i+1,cnt) {
				if(_sim(i,j))
					++tmp;
			}
			if( mmax < tmp )
				mmax = tmp;
		}
		printf("%d\n",mmax);
	}else
		printf("%d\n",cnt);
	return 0;
}
int main()
{
	while( scanf("%d",&N) , N ){
		work();
	}
	return 0;
}