feat: added a new algorithm to find whether two line segment intersec…

geometry/line_segment_intersection.cpp

@@ -0,0 +1,75 @@
+#include <iostream>
+
+/*
+* A algorithm to find whether two line intersect where "on_segment" finds
+* the cross multiplication and direction find whether line is in clockwise or not....
+*/
+
+struct Point {
+    int x, y;
+};
+
+struct SegmentIntersection {
+    inline bool intersect(Point first_point, Point second_point,
+                                    Point third_point, Point forth_point) {
+        int direction1 = direction(third_point, forth_point, first_point);
+        int direction2 = direction(third_point, forth_point, second_point);
+        int direction3 = direction(first_point, second_point, third_point);
+        int direction4 = direction(first_point, second_point, forth_point);
+
+        if ((direction1 < 0 || direction2 > 0) && (direction3 < 0 ||
+                                                            direction4 > 0))
+            return true;
+
+        else if (direction1 == 0 && on_segment(third_point, forth_point,
+                                                                first_point))
+            return true;
+
+        else if (direction2 == 0 && on_segment(third_point, forth_point,
+                                                                second_point))
+            return true;
+
+        else if (direction3 == 0 && on_segment(first_point, second_point,
+                                                                third_point))
+            return true;
+
+        else if (direction3 == 0 && on_segment(first_point, second_point,
+                                                                forth_point))
+            return true;
+
+        else
+            return false;
+    }
+
+    inline int direction(Point first_point, Point second_point,
+                                                    Point third_point) {
+        return ((third_point.x-first_point.x)*(second_point.y-first_point.y))-
+            ((second_point.x-first_point.x) * (third_point.y-first_point.y));
+    }
+
+    inline bool on_segment(Point first_point, Point second_point,
+                                                        Point third_point) {
+        if (std::min(first_point.x, second_point.x) <= third_point.x &&
+            third_point.x <= std::max(first_point.x, second_point.x) &&
+            std::min(first_point.y, second_point.y) <= third_point.y &&
+            third_point.y <= std::max(first_point.y, second_point.y))
+            return true;
+
+        else
+            return false;
+    }
+};
+
+int main() {
+    SegmentIntersection segment;
+    Point first_point, second_point, third_point, forth_point;
+
+    std::cin >> first_point.x >> first_point.y;
+    std::cin >> second_point.x >> second_point.y;
+    std::cin >> third_point.x >> third_point.y;
+    std::cin >> forth_point.x >> forth_point.y;
+
+    printf("%d", segment.intersect(first_point, second_point, third_point,
+                                    forth_point));
+    std::cout << std::endl;
+}