From e92f2cf3cfd633c1bcfd4a1cd68cfd870e01bc60 Mon Sep 17 00:00:00 2001
From: Yuri Gorshenin <y@maps.me>
Date: Mon, 15 Aug 2016 16:03:32 +0300
Subject: [search] Implemented clustering.

---
 search/nearby_points_sweeper.hpp | 124 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 124 insertions(+)
 create mode 100644 search/nearby_points_sweeper.hpp

(limited to 'search/nearby_points_sweeper.hpp')

diff --git a/search/nearby_points_sweeper.hpp b/search/nearby_points_sweeper.hpp
new file mode 100644
index 0000000000..9fbeef7228
--- /dev/null
+++ b/search/nearby_points_sweeper.hpp
@@ -0,0 +1,124 @@
+#pragma once
+
+#include "base/assert.hpp"
+
+#include "std/algorithm.hpp"
+#include "std/cstdint.hpp"
+#include "std/limits.hpp"
+#include "std/set.hpp"
+#include "std/utility.hpp"
+#include "std/vector.hpp"
+
+namespace search
+{
+// This class can be used to sweep points on a plane that are too
+// close to each other.  Two points are considered to be "too close"
+// when Manhattan distance between them is less than or equal to some
+// preselected epsilon.
+class NearbyPointsSweeper
+{
+public:
+  explicit NearbyPointsSweeper(double eps);
+
+  // Adds a new point (|x|, |y|) on the plane. |index| is used to
+  // identify individual points, and will be reported for survived
+  // points during the Sweep phase.
+  void Add(double x, double y, size_t index);
+
+  // Emits indexes of all survived points. Complexity: O(n * log(n)),
+  // where n is the number of already added points.
+  template <typename TEmitter>
+  void Sweep(TEmitter && emitter)
+  {
+    sort(m_events.begin(), m_events.end());
+
+    set<pair<double, size_t>> line;
+
+    for (auto const & event : m_events)
+    {
+      switch (event.m_type)
+      {
+      case Event::TYPE_SEGMENT_START:
+      {
+        if (line.empty())
+        {
+          line.emplace(event.m_x, event.m_index);
+          break;
+        }
+
+        auto it = line.upper_bound(make_pair(event.m_x, numeric_limits<size_t>::max()));
+
+        bool add = true;
+        while (true)
+        {
+          if (line.empty())
+            break;
+
+          if (it == line.end())
+          {
+            --it;
+            continue;
+          }
+
+          double const x = it->first;
+          if (fabs(x - event.m_x) <= m_eps)
+          {
+            add = false;
+            break;
+          }
+
+          if (x + m_eps < event.m_x)
+            break;
+
+          if (it == line.begin())
+            break;
+
+          --it;
+        }
+
+        if (add)
+          line.emplace(event.m_x, event.m_index);
+
+        break;
+      }
+
+      case Event::TYPE_SEGMENT_END:
+      {
+        auto it = line.find(make_pair(event.m_x, event.m_index));
+        if (it != line.end())
+        {
+          emitter(event.m_index);
+          line.erase(it);
+        }
+        break;
+      }
+      };
+    }
+
+    ASSERT(line.empty(), ("Sweep line must be empty after events processing:", line));
+  }
+
+private:
+  struct Event
+  {
+    enum Type
+    {
+      TYPE_SEGMENT_START,
+      TYPE_SEGMENT_END
+    };
+
+    Event(Type type, double y, double x, size_t index);
+
+    bool operator<(Event const & rhs) const;
+
+    Type m_type;
+
+    double m_y;
+    double m_x;
+    size_t m_index;
+  };
+
+  vector<Event> m_events;
+  double const m_eps;
+};
+}  // namespace search
-- 
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