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#1945. 寻找 Polly

Statistiques

Polly Polygon 在哪里?她正身处一片直线构成的原野之中。

给定一组直线,计算有多少个非自交多边形可以由每条直线各取一条线段构成。平凡线段(即长度为 0 的线段)不计入。多边形必须包含与原野中直线数量完全相同的不同顶点。

输入格式

第一行包含一个整数 $n$ ($3 \le n \le 12$),表示平面上的直线数量。

接下来的 $n$ 行,每行包含四个整数坐标值 $x_1, y_1, x_2$ 和 $y_2$(均在 $-2,000$ 到 $2,000$ 之间,含边界),表示一条经过点 $(x_1, y_1)$ 和 $(x_2, y_2)$ 的直线。注意,它们描述的是无限延伸的直线,而不仅仅是线段。所有直线均为不同的直线。定义直线的两个点也是不同的。

输入的直线可能平行。可能存在多条直线交于同一点的情况。直线之间的交点坐标可能大于 $2,000$。

输出格式

输出一个整数,表示可以由每条直线各取一条线段构成的非自交多边形的数量。

样例

样例输入 1

4
0 0 0 1
0 0 1 0
0 2 1 0
2 0 0 1

样例输出 1

2

样例输入 2

7
0 0 0 1
1 0 1 1
2 0 2 1
0 0 1 0
0 1 1 1
0 2 1 2
0 3 1 3

样例输出 2

0

样例输入 3

4
0 1 0 -1
1 0 -1 0
1 1 -1 -1
1 -1 -1 1

样例输出 3

0

Editorials

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