feat: add quiz 3 cross-checker.

cross-checker/include/cross-checker.h

@@ -0,0 +1,38 @@
+//
+// Created by ricardo on 19/05/25.
+//
+
+#ifndef CROSS_CHECKER_H
+#define CROSS_CHECKER_H
+
+namespace cross_checker
+{
+    // 既可以表示点也可以表示一个向量
+    struct Point
+    {
+        double x;
+        double y;
+
+        Point(const double a, const double b) : x(a), y(b)
+        {
+        }
+
+        static int orientation(const Point& p, const Point& q, const Point& r);
+
+        static bool onSegment(const Point& p, const Point& q, const Point& r);
+    };
+
+    struct Line
+    {
+        Point startPoint;
+        Point endPoint;
+
+        Line(const Point a, const Point b): startPoint(a), endPoint(b)
+        {
+        }
+
+        bool intersect(const Line& other);
+    };
+}
+
+#endif //CROSS_CHECKER_H