Implemented quad tree, added test project.

Game/Assets/Scripts/Model/IPositionable.cs

@@ -0,0 +1,12 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace TransportGame.Model
+{
+    public interface IPositionable
+    {
+        Vector2 Position { get; }
+    }
+}

Game/Assets/Scripts/Model/IPositionable.cs.meta

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+guid: cdecfb69b7ca68446910d0a607e934e6
+timeCreated: 1432824088
+licenseType: Free
+MonoImporter:
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
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Game/Assets/Scripts/Model/Point.cs

@@ -1,23 +0,0 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-
-namespace TransportGame.Model
-{
-    public class Point
-    {
-        public int X { get; set; }
-        public int Y { get; set; }
-
-        public Point()
-        {
-        }
-
-        public Point(int x, int y)
-        {
-            X = x;
-            Y = y;
-        }
-    }
-}

Game/Assets/Scripts/Utils/QuadTree.cs

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+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using TransportGame.Model;
+
+namespace TransportGame.Utils
+{
+    public class QuadTree<T>: ICollection<T> where T : IPositionable
+    {
+        private const int Capacity = 8;
+
+        /// <summary>
+        /// Gets the subtree in northwest position
+        /// </summary>
+        public QuadTree<T> NorthWest { get; private set; }
+
+        /// <summary>
+        /// Gets the subtree in northeast position
+        /// </summary>
+        public QuadTree<T> NorthEast { get; private set; }
+
+        /// <summary>
+        /// Gets the subtree in southeast position
+        /// </summary>
+        public QuadTree<T> SouthEast { get; private set; }
+
+        /// <summary>
+        /// Gets the subtree in southwest position
+        /// </summary>
+        public QuadTree<T> SouthWest { get; private set; }
+
+        /// <summary>
+        /// Gets the boundary of this quad tree
+        /// </summary>
+        public Rectangle Boundary { get; private set; }
+
+        private List<T> points = new List<T>(Capacity);
+
+        /// <summary>
+        /// Initializes a quad tree using specified boundaries
+        /// </summary>
+        /// <param name="left">Left</param>
+        /// <param name="top">Top</param>
+        /// <param name="right">Right</param>
+        /// <param name="bottom">Bottom</param>
+        public QuadTree(float left, float top, float right, float bottom)
+        {
+            Boundary = new Rectangle(left, top, right, bottom);
+        }
+
+        /// <summary>
+        /// Initializes a quad tree using specified boundaries
+        /// </summary>
+        /// <param name="boundary">Boundaries</param>
+        public QuadTree(Rectangle boundary)
+        {
+            Boundary = boundary;
+        }
+
+        private void Subdivide()
+        {
+            float midx = Boundary.Left + Boundary.Width / 2f;
+            float midy = Boundary.Top + Boundary.Height / 2f;
+
+            NorthWest = new QuadTree<T>(Boundary.Left, Boundary.Top, midx, midy);
+            NorthEast = new QuadTree<T>(midx, Boundary.Top, Boundary.Right, midy);
+            SouthEast = new QuadTree<T>(midx, midy, Boundary.Right, Boundary.Bottom);
+            SouthWest = new QuadTree<T>(Boundary.Left, midy, midx, Boundary.Bottom);
+
+            foreach (var point in points)
+                Add(point);
+
+            points.Clear();
+        }
+
+        private void Merge()
+        {
+            foreach (var point in NorthWest)
+                points.Add(point);
+
+            foreach (var point in NorthEast)
+                points.Add(point);
+
+            foreach (var point in SouthEast)
+                points.Add(point);
+
+            foreach (var point in SouthWest)
+                points.Add(point);
+
+            NorthWest = null;
+            NorthEast = null;
+            SouthEast = null;
+            SouthWest = null;
+        }
+
+        /// <summary>
+        /// Adds a point in this quad tree
+        /// </summary>
+        /// <param name="item">Point</param>
+        public void Add(T item)
+        {
+            // Precondition - point must be inside boundaries
+            if (!Boundary.Contains(item.Position))
+                throw new ArgumentException("Point must be inside boundaries.");
+
+            // Reached capacity, subdivide
+            if (NorthWest == null && points.Count >= Capacity)
+                Subdivide();
+
+            // Not divided in subtrees
+            if (NorthWest == null)
+            {
+                if (!points.Any(p => p.Position.Equals(item.Position)))
+                    points.Add(item);
+            }
+
+            // Add in the right subtree
+            else
+            {
+                if (NorthWest.Boundary.Contains(item.Position))
+                    NorthWest.Add(item);
+
+                else if (NorthEast.Boundary.Contains(item.Position))
+                    NorthEast.Add(item);
+
+                else if (SouthEast.Boundary.Contains(item.Position))
+                    SouthEast.Add(item);
+
+                else SouthWest.Add(item);
+            }
+        }
+
+        /// <summary>
+        /// Empties the entire tree
+        /// </summary>
+        public void Clear()
+        {
+            NorthWest = null; 
+            NorthEast = null;
+            SouthEast = null;
+            SouthWest = null;
+            points.Clear();
+        }
+
+        /// <summary>
+        /// Tests if specified point is contained in this tree
+        /// </summary>
+        /// <param name="item">Point</param>
+        /// <returns>True if point is contained</returns>
+        public bool Contains(T item)
+        {
+            if (NorthWest == null)
+                return points.Contains(item);
+            else
+                return NorthWest.Contains(item) || NorthEast.Contains(item) || SouthEast.Contains(item) || SouthWest.Contains(item);
+        }
+
+        /// <summary>
+        /// Copies all points to specified array
+        /// </summary>
+        /// <param name="array">Array</param>
+        /// <param name="arrayIndex">Index where to start copying</param>
+        public void CopyTo(T[] array, int arrayIndex)
+        {
+            foreach (var point in this)
+                array[arrayIndex++] = point;
+        }
+
+        /// <summary>
+        /// Gets the number of points in this quad tree
+        /// </summary>
+        public int Count
+        {
+            get 
+            {
+                return (NorthWest == null) ? points.Count : NorthWest.Count + NorthEast.Count + SouthEast.Count + SouthWest.Count;
+            }
+        }
+
+        /// <summary>
+        /// Returns true if this container is read-only.
+        /// </summary>
+        public bool IsReadOnly
+        {
+            get 
+            {
+                return false;
+            }
+        }
+
+        /// <summary>
+        /// Removes an item from the tree
+        /// </summary>
+        /// <param name="item">Item to remove</param>
+        /// <returns>True if item was removed</returns>
+        public bool Remove(T item)
+        {
+            if (NorthWest == null)
+                return points.Remove(item);
+
+            else
+            {
+                bool result = NorthWest.Remove(item) || NorthEast.Remove(item) || SouthEast.Remove(item) || SouthWest.Remove(item);
+                
+                // We can merge subdivisions
+                if (Count < (Capacity - Capacity / 3))
+                    Merge();
+
+                return result;
+            }
+        }
+
+        /// <summary>
+        /// Gets an enumerator for this collection
+        /// </summary>
+        /// <returns></returns>
+        System.Collections.IEnumerator IEnumerable.GetEnumerator()
+        {
+            foreach (var point in this)
+                yield return point;
+        }
+
+        /// <summary>
+        /// Gets enumerator for this collection
+        /// </summary>
+        /// <returns></returns>
+        public IEnumerator<T> GetEnumerator()
+        {
+            if (NorthWest == null)
+            {
+                foreach (var point in points)
+                    yield return point;
+            }
+
+            else
+            {
+                foreach (var point in NorthWest)
+                    yield return point;
+
+                foreach (var point in NorthEast)
+                    yield return point;
+
+                foreach (var point in SouthEast)
+                    yield return point;
+
+                foreach (var point in SouthWest)
+                    yield return point;
+            }
+        }
+
+        /// <summary>
+        /// Gets all the points in the specified region
+        /// </summary>
+        /// <param name="rect">Region</param>
+        /// <returns>Points</returns>
+        public IEnumerable<T> Query(Rectangle rect)
+        {
+            // No intersection
+            if (!Rectangle.Intersects(rect, Boundary))
+                return Enumerable.Empty<T>();
+
+            if (NorthWest == null)
+            {
+                return points.Where(p => rect.Contains(p.Position));
+            }
+            else
+            {
+                return NorthWest.Query(rect)
+                    .Concat(NorthEast.Query(rect))
+                    .Concat(SouthEast.Query(rect))
+                    .Concat(SouthWest.Query(rect));
+            }
+        }
+        
+        /// <summary>
+        /// Gets all the points in the specified region
+        /// </summary>
+        /// <param name="left">Left</param>
+        /// <param name="top">Top</param>
+        /// <param name="right">Right</param>
+        /// <param name="bottom">Bottom</param>
+        /// <returns>Points</returns>
+        public IEnumerable<T> Query(float left, float top, float right, float bottom)
+        {
+            return Query(new Rectangle(left, top, right, bottom));
+        }
+    }
+}

Game/Assets/Scripts/Utils/QuadTree.cs.meta

@@ -0,0 +1,12 @@
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+timeCreated: 1432824088
+licenseType: Free
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+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
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