Reverted line intersection

Author: lucashc

algorithms/intersection_line_segments.cpp

@@ -0,0 +1,32 @@
+# Intersection of line segments
+## \note Line segments are given by the coordinates of their end points.
+struct Point {
+
+	long long x, y;
+
+};
+
+struct Line {
+	Point p, q;
+};
+
+int sgn(long long x) {
+	return x == 0 ? 0 : (x < 0 ? -1 : 1);
+}
+
+long long det(long long x1, long long y1, long long x2, long long y2) {
+	return x1 * y2 - x2 * y1;
+}
+
+int orientation(Point p, Point q, Point r) {
+	return sgn(det(p.x - r.x, p.y - r.y, q.x - r.x, q.y - r.y));
+}
+
+bool intersect(Line l1, Line l2) {
+	if (max(l1.p.x, l1.q.x) < min(l2.p.x, l2.q.x)) return false;
+	if (max(l2.p.x, l2.q.x) < min(l1.p.x, l1.q.x)) return false;
+	if (max(l1.p.y, l1.q.y) < min(l2.p.y, l2.q.y)) return false;
+	if (max(l2.p.y, l2.q.y) < min(l1.p.y, l1.q.y)) return false;
+	return orientation(l1.q, l2.p, l1.p) * orientation(l1.q, l2.q, l1.p) <= 0
+		&& orientation(l2.q, l1.p, l2.p) * orientation(l2.q, l1.q, l2.p) <= 0;
+}