POJ_3668

    可以先将所有的直线求出来，然后按斜率排个序，之后顺序扫描一遍就可以统计出结果了。

#include
     
      #include
      
       #include
       
        #define MAXD 210struct Point{    int x, y;    bool operator < (const Point &t) const    {        if(x == t.x) return y < t.y;        return x < t.x;    }}p[MAXD];struct Vector{    int x, y;    bool operator < (const Vector &t) const    {        return y * t.x < x * t.y;    }    bool operator != (const Vector &t) const    {        return y * t.x != x * t.y;    }}a[MAXD * MAXD];int N;void init(){    int i;    for(i = 0; i < N; i ++) scanf("%d%d", &p[i].x, &p[i].y);}void solve(){    int i, j, n = 0, cnt;    std::sort(p, p + N);    for(i = 0; i < N; i ++)        for(j = i + 1; j < N; j ++)            a[n].x = p[j].x - p[i].x, a[n].y = p[j].y - p[i].y, ++ n;    std::sort(a, a + n);    for(i = cnt = 1; i < n; i ++)        if(a[i] != a[i - 1]) ++ cnt;    printf("%d\n", cnt);}int main(){    while(scanf("%d", &N) == 1)    {        init();        solve();    }    return 0;}