Added DisjointSets and DisjointSets<T> collections

Main/src/CodeJam.Main.csproj

@@ -74,6 +74,9 @@
       <DesignTime>True</DesignTime>
       <DependentUpon>DebugCode.tt</DependentUpon>
     </Compile>
+    <Compile Include="Collections\DisjointSets.cs" />
+    <Compile Include="Collections\DisjointSetsBase.cs" />
+    <Compile Include="Collections\DisjointSetsT.cs" />
     <Compile Include="Collections\EnumerableExtensions.Index.cs" />
     <Compile Include="Collections\IndexedItem.cs" />
     <Compile Include="Collections\EnumerableExtensions.Page.cs" />

Main/src/Collections/DisjointSets.cs

@@ -0,0 +1,30 @@
+namespace CodeJam.Collections
+{
+	/// <summary>Disjoint sets without payload</summary>
+	///  <remarks>
+	/// See http://en.wikipedia.org/wiki/Disjoint-set_data_structure
+	/// </remarks>
+	public sealed class DisjointSets : DisjointSetsBase<BasicNode>
+	{
+		/// <summary>Creates an empty Disjoint sets</summary>
+		public DisjointSets() { }
+
+		/// <summary>Creates a Disjoint sets with the given number of elements</summary>
+		/// <param name="count">The initial number of elements</param>
+		public DisjointSets(int count)
+		{
+			Add(count);
+		}
+
+		/// <summary>Appends the given number of new elements</summary>
+		/// <param name="count">The number of elements to add</param>
+		public void Add(int count)
+		{
+			for (var i = 0; i < count; ++i)
+			{
+				Nodes_.Add(new BasicNode { ParentIndex = -1, Rank = 0 });
+			}
+			SetsCount += count;
+		}
+	}
+}

Main/src/Collections/DisjointSetsBase.cs

@@ -0,0 +1,104 @@
+using System.Collections.Generic;
+
+namespace CodeJam.Collections
+{
+	/// <summary>Disjoint sets implementation base</summary>
+	///  <remarks>
+	/// See http://en.wikipedia.org/wiki/Disjoint-set_data_structure
+	/// </remarks>
+	public class DisjointSetsBase<T> where T : BasicNode
+	{
+		/// <summary>All nodes</summary>
+		protected readonly List<T> Nodes_ = new List<T>();
+
+		/// <summary>Creates an empty base</summary>
+		protected DisjointSetsBase() { }
+
+		/// <summary>The number of nodes</summary>
+		public int Count => Nodes_.Count;
+
+		/// <summary>The number of disjoint sets</summary>
+		public int SetsCount { get; protected set; }
+
+		/// <summary>Finds a set identifier for the element</summary>
+		/// <param name="index">The element index</param>
+		/// <returns>The identifier of the containing set</returns>
+		/// <remarks>
+		/// The set identifier is the index of a single element representing the set.
+		/// The Union operation may lead to a choice of a different representative for a set.
+		/// In this case IndexToSetId(oldSetId) may be called to get the new set id.
+		/// </remarks>
+		public int IndexToSetId(int index)
+		{
+			// First, find a root element of a tree containing the passed element
+			var rootIndex = index;
+			for (;;)
+			{
+				var parentIndex = Nodes_[rootIndex].ParentIndex;
+				if (parentIndex == -1)
+				{
+					break;
+				}
+				rootIndex = parentIndex;
+			}
+
+			// Then, do the path compression:
+			// walk from the passed element upto the root replacing the the ParentIndex with the root index
+			while (index != rootIndex)
+			{
+				var node = Nodes_[index];
+				index = node.ParentIndex;
+				node.ParentIndex = rootIndex;
+			}
+			return rootIndex;
+		}
+
+		/// <summary>Combines to distjoint sets into a single set</summary>
+		/// <param name="elementOfSet1Index">Index of an element of the first set</param>
+		/// <param name="elementOfSet2Index">Index of an element of the second set</param>
+		public void Union(int elementOfSet1Index, int elementOfSet2Index)
+		{
+			elementOfSet1Index = IndexToSetId(elementOfSet1Index);
+			elementOfSet2Index = IndexToSetId(elementOfSet2Index);
+			if (elementOfSet1Index == elementOfSet2Index)
+			{
+				return; // Already the single set
+			}
+
+			var set1Root = Nodes_[elementOfSet1Index];
+			var set2Root = Nodes_[elementOfSet2Index];
+			var rankDifference = set1Root.Rank - set2Root.Rank;
+			// Attach the tree with a smaller rank to the tree with a higher rank.
+			// The resulting tree rank is equal to the higher rank
+			// except the case when initial ranks are equal.
+			// In the latter case the new rank will be increased by 1
+			if (rankDifference > 0) // 1st has higher rank
+			{
+				set2Root.ParentIndex = elementOfSet1Index;
+			}
+			else if (rankDifference < 0) // 2nd has the higher rank
+			{
+				set1Root.ParentIndex = elementOfSet2Index;
+			}
+			else // ranks are equal and the new root choice is arbitrary
+			{
+				set2Root.ParentIndex = elementOfSet1Index;
+				++set1Root.Rank;
+			}
+
+			// we have joined 2 sets, so we have to decrease the count
+			--SetsCount;
+		}
+	}
+
+	/// <summary>Node base class</summary>
+	public class BasicNode
+	{
+		/// <summary>Parent node index</summary>
+		/// <remarks>Points to the root after a path compression</remarks>
+		public int ParentIndex;
+
+		/// <summary>Estimated height of the tree (i.e. maximum length of the path from the root to a node. Path compression is not taken into account)</summary>
+		public int Rank;
+	}
+}

Main/src/Collections/DisjointSetsT.cs

@@ -0,0 +1,52 @@
+using System.Collections.Generic;
+using System.Linq;
+
+namespace CodeJam.Collections
+{
+	/// <summary>
+	/// Generic implementation of the Disjoint sets
+	/// </summary>
+	///  <remarks>
+	/// See http://en.wikipedia.org/wiki/Disjoint-set_data_structure
+	/// </remarks>
+	public sealed class DisjointSets<T> : DisjointSetsBase<DisjointSets<T>.Node>
+	{
+		/// <summary>Creates an empty Disjoint sets</summary>
+		public DisjointSets() { }
+
+		/// <summary>Creates a Disjoint sets with the passed values</summary>
+		/// <param name="values">The values to store</param>
+		public DisjointSets(IEnumerable<T> values)
+		{
+			Add(values);
+		}
+
+		/// <summary>Gets an element by its index</summary>
+		/// <param name="index">Elmement's index</param>
+		public T this[int index] => Nodes_[index].Value;
+
+		/// <summary>Appends a list of values</summary>
+		/// <param name="values">The values to append</param>
+		public void Add(IEnumerable<T> values)
+		{
+			var initialNodesCount = Nodes_.Count;
+			Nodes_.AddRange(values.Select(_ => new Node { Value = _, ParentIndex = -1, Rank = 0 }));
+			SetsCount += Nodes_.Count - initialNodesCount;
+		}
+
+		/// <summary>Appends a single element</summary>
+		/// <param name="value">The value to append</param>
+		public void Add(T value)
+		{
+			Nodes_.Add(new Node { Value = value, ParentIndex = -1, Rank = 0 });
+			++SetsCount;
+		}
+
+		/// <summary>A sets node</summary>
+		public class Node : BasicNode
+		{
+			/// <summary>The node data</summary>
+			public T Value;
+		}
+	}
+}

Main/tests/CodeJam.Main-Tests.csproj

@@ -59,6 +59,7 @@
     <Compile Include="Assertions\CodeAssertionsTest.cs" />
     <Compile Include="Collections\AggregateFuncsTest.cs" />
     <Compile Include="Collections\ArrayExtensionsTest.cs" />
+    <Compile Include="Collections\DisjointSetsTest.cs" />
     <Compile Include="Collections\QueryableExtensionsTests.ApplyOrder.cs" />
     <Compile Include="Collections\DictionaryExtensionsTest.cs" />
     <Compile Include="Collections\AggregateFuncsTest.generated.cs">

Main/tests/Collections/DisjointSetsTest.cs

@@ -0,0 +1,65 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+using CodeJam.Collections;
+
+using NUnit.Framework;
+
+namespace Tests
+{
+	[TestFixture]
+	public class DisjointSetsTest
+	{
+		private readonly Random random_ = new Random();
+		private const int ElementsNumber = 10000;
+		private readonly List<int> seq_ = Enumerable.Range(0, ElementsNumber).ToList();
+
+		[Test]
+		public void Test01NonGeneric()
+		{
+			for (var i = 1; i <= ElementsNumber; i += 1 + i / (10 + random_.Next(0, 10)))
+			{
+				Console.WriteLine("i = {0}", i);
+				var djs = new DisjointSets(ElementsNumber);
+				foreach (var el in RandomShuffle(seq_))
+				{
+					djs.Union(el, el % i);
+				}
+				VerifySets(djs, i);
+			}
+		}
+
+		[Test]
+		public void Test02Generic()
+		{
+			for (var i = 1; i <= ElementsNumber; i += 1 + i / (10 + random_.Next(0, 10)))
+			{
+				Console.WriteLine("i = {0}", i);
+				var rs = RandomShuffle(seq_).ToList();
+				var djs = new DisjointSets<int>(rs);
+				foreach (var el in rs)
+				{
+					djs.Union(el, el % i);
+				}
+				VerifySets(djs, i);
+				for (var j = 0; j < ElementsNumber; ++j)
+				{
+					Assert.That(djs[j], Is.EqualTo(rs[j]));
+				}
+			}
+		}
+
+		private static void VerifySets<T>(DisjointSetsBase<T> djs, int mod) where T : BasicNode
+		{
+			Assert.That(djs.Count, Is.EqualTo(ElementsNumber));
+			Assert.That(djs.SetsCount, Is.EqualTo(mod));
+			for (var i = 0; i < ElementsNumber; ++i)
+			{
+				Assert.That(djs.IndexToSetId(i), Is.EqualTo(djs.IndexToSetId(i % mod)), "i = {0}, mod = {1}", i, mod);
+			}
+		}
+
+		private IEnumerable<T> RandomShuffle<T>(IEnumerable<T> en) => en.OrderBy(x => random_.Next());
+	}
+}