判断两条线段是否有交点（附HDU - 1086 You can Solve a Geometry Problem too代码）

Segment-Intersection.cpp

@@ -0,0 +1,57 @@
+#include <cstdio>
+
+using namespace std;
+
+struct point
+{
+	double x, y;
+	point() { }
+	point(double _x, double _y) : x(_x), y(_y) { }
+};
+
+struct segment
+{
+	point s, t;
+	segment() { }
+	segment(point _s, point _t) : s(_s), t(_t) { }
+}s[110];
+
+double cross(segment base, segment x)
+{
+	return (base.s.x - base.t.x) * (x.s.y - x.t.y) - (base.s.y - base.t.y) * (x.s.x - x.t.x);
+}
+
+bool segment_intersect(segment x, segment y)
+{
+	return cross(x, segment(x.s, y.s)) * cross(x, segment(x.s, y.t)) <= 0 && cross(y, segment(y.s, x.s)) * cross(y, segment(y.s, x.t)) <= 0;
+}
+
+int main()
+{
+	int m;
+	while (true)
+	{
+		scanf("%d", &m);
+		if (m == 0)
+		{
+			break;
+		}
+		for (int i = 0; i < m; i++)
+		{
+			scanf("%lf%lf%lf%lf", &s[i].s.x, &s[i].s.y, &s[i].t.x, &s[i].t.y);
+		}
+		int ans = 0;
+		for (int i = 0; i < m; i++)
+		{
+			for (int j = 0; j < i; j++)
+			{
+				if (segment_intersect(s[i], s[j]) == true)
+				{
+					ans++;
+				}
+			}
+		}
+		printf("%d\n", ans);
+	}
+	return 0;
+}