Feature Request : Adding best and efficient LineIntersection java code in Geometry #Hacktoberfest

src/main/java/com/thealgorithms/geometry/LineIntersection.java

@@ -0,0 +1,70 @@
+package com.thealgorithms.geometry;
+
+/**
+ * Utility class to check if two line segments intersect.
+ *
+ * <p>This class provides methods to determine whether two given line segments
+ * intersect or not, using orientation tests.
+ *
+ * <p>Time Complexity: O(1)
+ *
+ * @author Sandeep
+ */
+public final class LineIntersection {
+
+    private LineIntersection() {
+    }
+
+    /**
+     * Represents a point in 2D space.
+     */
+    public static final class Point {
+        public final double x;
+        public final double y;
+
+        public Point(double x, double y) {
+            this.x = x;
+            this.y = y;
+        }
+    }
+
+    private static int orientation(Point p, Point q, Point r) {
+        double val = (q.y - p.y) * (r.x - q.x) - (q.x - p.x) * (r.y - q.y);
+        if (val == 0.0) {
+            return 0; // collinear
+        }
+        return (val > 0.0) ? 1 : 2; // clockwise or counterclockwise
+    }
+
+    private static boolean onSegment(Point p, Point q, Point r) {
+        return q.x <= Math.max(p.x, r.x) && q.x >= Math.min(p.x, r.x)
+            && q.y <= Math.max(p.y, r.y) && q.y >= Math.min(p.y, r.y);
+    }
+
+    /**
+     * Checks whether two line segments (p1,q1) and (p2,q2) intersect.
+     *
+     * @param p1 starting point of first segment
+     * @param q1 ending point of first segment
+     * @param p2 starting point of second segment
+     * @param q2 ending point of second segment
+     * @return true if the segments intersect, false otherwise
+     */
+    public static boolean doIntersect(Point p1, Point q1, Point p2, Point q2) {
+        int o1 = orientation(p1, q1, p2);
+        int o2 = orientation(p1, q1, q2);
+        int o3 = orientation(p2, q2, p1);
+        int o4 = orientation(p2, q2, q1);
+
+        if (o1 != o2 && o3 != o4) {
+            return true;
+        }
+
+        if (o1 == 0 && onSegment(p1, p2, q1)) return true;
+        if (o2 == 0 && onSegment(p1, q2, q1)) return true;
+        if (o3 == 0 && onSegment(p2, p1, q2)) return true;
+        if (o4 == 0 && onSegment(p2, q1, q2)) return true;
+
+        return false;
+    }
+}

src/test/java/com/thealgorithms/geometry/LineIntersectionTest.java

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+package com.thealgorithms.geometry;
+
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.*;
+
+public class LineIntersectionTest {
+
+    @Test
+    void testIntersectingSegments() {
+        LineIntersection.Point p1 = new LineIntersection.Point(1, 1);
+        LineIntersection.Point q1 = new LineIntersection.Point(4, 4);
+        LineIntersection.Point p2 = new LineIntersection.Point(1, 4);
+        LineIntersection.Point q2 = new LineIntersection.Point(4, 1);
+        assertTrue(LineIntersection.doIntersect(p1, q1, p2, q2));
+    }
+
+    @Test
+    void testNonIntersectingSegments() {
+        LineIntersection.Point p1 = new LineIntersection.Point(1, 1);
+        LineIntersection.Point q1 = new LineIntersection.Point(2, 2);
+        LineIntersection.Point p2 = new LineIntersection.Point(3, 3);
+        LineIntersection.Point q2 = new LineIntersection.Point(4, 4);
+        assertFalse(LineIntersection.doIntersect(p1, q1, p2, q2));
+    }
+
+    @Test
+    void testCollinearOverlappingSegments() {
+        LineIntersection.Point p1 = new LineIntersection.Point(1, 1);
+        LineIntersection.Point q1 = new LineIntersection.Point(5, 5);
+        LineIntersection.Point p2 = new LineIntersection.Point(2, 2);
+        LineIntersection.Point q2 = new LineIntersection.Point(6, 6);
+        assertTrue(LineIntersection.doIntersect(p1, q1, p2, q2));
+    }
+}