hdu 1154& Poj2462 Cutting a Polygon 计算几何模板集合

题目链接：

http://acm.hdu.edu.cn/showproblem.php?pid=1154

用到了直线与线段的关系，直线与线段的交点，点是否在多边形内部，点是否在线段上等的模板

Cutting a Polygon Time Limit: 1000MS   Memory Limit: 65536K Total Submissions: 878   Accepted: 256 Description Given is a simple but not necessarily convex polygon. Given is also a line in the plane. If the polygon is cut along the line then we may get several smaller polygons. Your task is to find the length of the cut, that is the total length of the segments in the intersection of the line and the polygon. Input Input consists of a number of cases. The data of each case appears on a number of input lines, the first of which contains two non negative integers n and m giving the number of the vertices of the polygon and the number of cutting lines to consider, 3 <= n <= 1000. The following n lines contain coordinates of the vertices of the polygon; each line contains the x and y coordinates of a vertex. The vertices are given either in clockwise or counterclockwise order. Each of the following m lines of input contains four numbers; these are x and y coordinates of the two points defining the cutting line. If a vertex of the polygon is closer than 1e-8 to the cutting line then we consider that the vertex lies on the cutting line.  Input is terminated by a line with n and m equal to 0.  Output For each cutting line, print the total length of the segments in the intersection of the line and the polygon defined for this test case, with 3 digits after the decimal point. Note: the perimiter of a polygon belongs to the polygon.  The picture above illustrates the first cutting line for the polygon from the sample. Sample Input 9 5 0 0 0 2 1 1 2 2 3 1 4 2 5 1 6 2 6 0 -1 2 7.5 1 0 1 6 1 0 1.5 6 1.5 0 2 6 1 0 0 0 2 0 0 Sample Output 2.798 6.000 3.000 2.954 2.000 Source Waterloo local 2005.06.11

 

 题目大意：

给你一个由n个点构成的多边行，然后一条直线穿过这个多边行，问直线与多边形相交的相邻的点构成线段在多边行内部的长度，即：有多长的线段在多变形内部。

思路，寻找直线与多边形的所有交点，然后判断交点的中点是否在多边形内部，累计求和，

//注意：G++输出要用%0.3f

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