temp check

Author: pllee4

src/generic/CMakeLists.txt

@@ -1,3 +1,4 @@
 add_subdirectory(common)
+add_subdirectory(convex_hull)
 add_subdirectory(digital_filter)
 add_subdirectory(polynomial)

src/generic/convex_hull/CMakeLists.txt

@@ -0,0 +1 @@
+add_executable(test_convex_hull convex_hull.cpp)

src/generic/convex_hull/convex_hull.cpp

@@ -0,0 +1,183 @@
+#include <algorithm>
+#include <iostream>
+#include <optional>
+
+template <typename T>
+struct Point {
+  T x;
+  T y;
+};
+
+/**
+ * @brief Get the Cross Product of segment (a, b) and (a, c)
+ *
+ * Example:
+ *           W(3, 4)
+ *                      V(5, 2)
+ * (0,0)
+ *
+ * V x W = VxWy - WxVy
+ *     = | 5 3 |
+ *       | 2 4 |
+ *     = (5 * 4) - (2 * 3) = 14 (counter-clockwise)
+ *
+ * @tparam T
+ * @param a
+ * @param b
+ * @param c
+ * @return T positive for counter-clockwise, negative for clockwise, zero for
+ * collinear
+ */
+template <typename T>
+T GetCrossProduct(const Point<T> &a, const Point<T> &b, const Point<T> &c) {
+  return ((b.x - a.x) * (c.y - a.y) - (b.y - a.y) * (c.x - a.x));
+}
+
+template <typename T>
+Point<T> SwapAndGetFirstPoint(std::vector<Point<T>> &points) {
+  auto iterator = std::min_element(
+      points.begin(), points.end(), [](const Point<T> a, const Point<T> b) {
+        return ((a.y < b.y) || ((a.y == b.y) && (a.x < b.x)));
+      });
+  auto old_first_point = points[0];
+  points[0] = *iterator;
+  *iterator = old_first_point;
+  return points[0];
+}
+
+template <typename T>
+std::vector<Point<T>> GetConvexHull(std::vector<Point<T>> &points) {
+  if (points.size() < 3) {
+    return std::vector<Point<T>>{};
+  }
+  auto first_point = SwapAndGetFirstPoint(points);
+  std::sort(points.begin() + 1, points.end(),
+            [&](const Point<T> &b, const Point<T> &c) {
+              return (GetCrossProduct(first_point, b, c) < 0);
+            });
+
+  std::vector<Point<T>> result;
+  auto it = points.begin();
+
+  auto value = *it++;
+  std::cout << "Adding... " << value.x << " " << value.y << std::endl;
+
+  result.push_back(value);
+
+  value = *it++;
+  std::cout << "Adding... " << value.x << " " << value.y << std::endl;
+
+  result.push_back(value);
+
+  value = *it++;
+  std::cout << "Adding... " << value.x << " " << value.y << std::endl;
+
+  result.push_back(value);
+
+  while (it != points.end()) {
+    // StepConverge
+    // Pop off any points that make a convex angle with *it
+    while (GetCrossProduct(*(result.rbegin() + 1), *(result.rbegin()), *it) >=
+           0) {
+      std::cout << "Popping out: " << result.back().x << " " << result.back().y
+                << std::endl;
+      result.pop_back();
+    }
+
+    auto value = *it++;
+    std::cout << "Adding... " << value.x << " " << value.y << std::endl;
+    result.push_back(value);
+  }
+
+  return result;
+}
+
+template <typename T>
+class ConvexHull {
+ public:
+  using Callback = std::function<void(const Point<T> &)>;
+  explicit ConvexHull(const std::vector<Point<T>> &points)
+      : points_(points), current_index_(0) {
+    auto first_point = SwapAndGetFirstPoint(points_);
+    std::sort(points_.begin() + 1, points_.end(),
+              [&](const Point<T> &b, const Point<T> &c) {
+                return (GetCrossProduct(first_point, b, c) < 0);
+              });
+    initialize_first_three_points_ = true;
+  }
+
+  std::optional<std::vector<Point<T>>> StepForward(Callback insert_callback,
+                                                   Callback pop_callback) {
+    if (points_.size() < 3) {
+      return std::nullopt;
+    } else {
+      if (initialize_first_three_points_) {
+        for (auto i = 0; i < 3; ++i) {
+          InsertCurrentValueWithCallback(insert_callback);
+        }
+        initialize_first_three_points_ = false;
+        return std::nullopt;
+      }
+    }
+
+    if (current_index_ < points_.size()) {
+      if (GetCrossProduct(*(results_.rbegin() + 1), *(results_.rbegin()),
+                          points_.at(current_index_)) >= 0) {
+        PopCurrentValueWithCallback(pop_callback);
+      } else {
+        InsertCurrentValueWithCallback(insert_callback);
+      }
+    } else {
+      return results_;
+    }
+
+    return std::nullopt;
+  }
+
+ private:
+  void InsertCurrentValueWithCallback(Callback insert_callback) {
+    const auto value = points_.at(current_index_);
+    insert_callback(value);
+    results_.push_back(value);
+    current_index_++;
+  }
+
+  void PopCurrentValueWithCallback(Callback pop_callback) {
+    pop_callback(results_.back());
+    results_.pop_back();
+  }
+
+  std::vector<Point<T>> points_;
+  std::vector<Point<T>> results_;
+  size_t current_index_;
+  bool initialize_first_three_points_;
+};
+
+int main() {
+  auto points = std::vector<Point<int>>{{0, 3}, {1, 1}, {2, 2}, {4, 4},
+                                        {0, 0}, {1, 2}, {3, 1}, {3, 3}};
+  auto result = GetConvexHull(points);
+  std::cout << "Results" << std::endl;
+  for (const auto value : result) {
+    std::cout << value.x << " " << value.y << std::endl;
+  }
+
+  std::cout << "-------------------" << std::endl;
+  auto convex_hull = ConvexHull(points);
+  while (convex_hull.StepForward(
+             [](const Point<int> &point) {
+               std::cout << "Adding... " << point.x << " " << point.y
+                         << std::endl;
+             },
+             [](const Point<int> &point) {
+               std::cout << "Popping out: " << point.x << " " << point.y
+                         << std::endl;
+             }) == std::nullopt) {
+  }
+  auto new_result = convex_hull.StepForward([](const Point<int> &) {},
+                                            [](const Point<int> &) {});
+  std::cout << "Results" << std::endl;
+  for (const auto value : *new_result) {
+    std::cout << value.x << " " << value.y << std::endl;
+  }
+}