poj2780

同2606

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <algorithm>
using namespace std;

#define eps 1.0e-8
#define maxn 1005

struct XPoint
{
    int x, y;
} point[maxn];

struct Line
{
    int a, b;
    double k;
    bool end;
} line[maxn * maxn];

int n, ncount;

bool operator <(const Line &a, const Line &b)
{
    if (abs(a.k - b.k) > eps && !a.end && !b.end)
        return a.k < b.k;
    if (a.end != b.end)
        return a.end < b.end;
    if (a.a != b.a)
        return a.a < b.a;
    return a.b < b.b;
}

double getk(XPoint &a, XPoint &b)
{
    return (b.y - a.y) * 1.0 / (b.x - a.x);
}

int main()
{
    //freopen("t.txt", "r", stdin);
    while (~scanf("%d", &n))
    {
        ncount = 0;
        for (int i = 0; i < n; i++)
            scanf("%d%d", &point[i].x, &point[i].y);
        for (int i = 0; i < n - 1; i++)
            for (int j = i + 1; j < n; j++)
            {
                line[ncount].a = i;
                line[ncount].b = j;
                if (point[i].x == point[j].x)
                    line[ncount].end = true;
                else
                {
                    line[ncount].end = false;
                    line[ncount].k = getk(point[i], point[j]);
                }
                ncount++;
            }
        sort(line, line + ncount);
        int start = 0;
        int ans = 0;
        for (int i = 1; i < ncount; i++)
        {
            if (!((line[i].end && line[start].end) || ((!line[i].end && !line[start].end) && (line[i].k - line[start].k) < eps)) || line[i].a != line[start].a)
            {
                start = i;
                continue;
            }
            if (i - start > ans)
            {
                ans = i - start;
            }
        }
        printf("%d\n", ans + 2);
    }
    return 0;
}