Add less than operator for Point2

src/Point2.cpp

@@ -65,6 +65,11 @@ bool Point2::operator!=(const Point2& rhs) const
     return !(*this == rhs);
 }
 
+bool Point2::operator<(const Point2& rhs) const
+{
+    return x < rhs.x || (x == rhs.x && y < rhs.y);
+}
+
 Point2 Point2::operator+(const Point2& rhs) const
 {
     return Point2(x + rhs.x, y + rhs.y);