HW4 SkipList

HW4/HW4.sln

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+
+Microsoft Visual Studio Solution File, Format Version 12.00
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "SkipList", "SkipList\SkipList.csproj", "{CE9E0C67-54C7-4201-A3DC-23973756923D}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "SkipListTests", "SkipListTests\SkipListTests.csproj", "{25793A21-4C06-4F61-902A-E9F69D44B820}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{CE9E0C67-54C7-4201-A3DC-23973756923D}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{CE9E0C67-54C7-4201-A3DC-23973756923D}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{CE9E0C67-54C7-4201-A3DC-23973756923D}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{CE9E0C67-54C7-4201-A3DC-23973756923D}.Release|Any CPU.Build.0 = Release|Any CPU
+		{25793A21-4C06-4F61-902A-E9F69D44B820}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{25793A21-4C06-4F61-902A-E9F69D44B820}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{25793A21-4C06-4F61-902A-E9F69D44B820}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{25793A21-4C06-4F61-902A-E9F69D44B820}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+EndGlobal

HW4/SkipList/SkipList.cs

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+// <copyright file="SkipList.cs" company="khusainovilas">
+// Copyright (c) khusainovilas. All rights reserved.
+// </copyright>
+
+namespace SkipList;
+
+using System.Collections;
+
+/// <summary>
+/// Skip list implementation.
+/// </summary>
+/// <typeparam name="T">Type of elements in the list.</typeparam>
+public class SkipList<T> : IList<T>
+    where T : IComparable<T>
+{
+    private const int MaxLevel = 16;
+    private readonly Random random = new();
+    private readonly SkipListNode sentinel = new(default, null, null);
+    private SkipListNode header;
+    private SkipListNode baseHeader;
+    private int currentVersion;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="SkipList{T}"/> class.
+    /// </summary>
+    public SkipList()
+    {
+        this.baseHeader = new SkipListNode(default, this.sentinel, this.sentinel);
+        var curr = this.baseHeader;
+        for (var level = 0; level < MaxLevel; level++)
+        {
+            curr = new SkipListNode(default, this.sentinel, curr);
+        }
+
+        this.header = curr;
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="SkipList{T}"/> class with elements from a collection.
+    /// </summary>
+    /// <param name="collection">The collection to initialize from.</param>
+    public SkipList(IEnumerable<T> collection)
+        : this()
+    {
+        ArgumentNullException.ThrowIfNull(collection);
+        foreach (var element in collection)
+        {
+            this.Add(element);
+        }
+    }
+
+    /// <inheritdoc/>
+    public int Count { get; private set; }
+
+    /// <inheritdoc/>
+    public bool IsReadOnly => false;
+
+    /// <inheritdoc/>
+    public T this[int index]
+    {
+        get
+        {
+            if (index < 0 || index >= this.Count)
+            {
+                throw new ArgumentOutOfRangeException(nameof(index));
+            }
+
+            var curr = this.baseHeader.Next ?? throw new SkipListException("Cannot access item in empty skip list.");
+            for (var i = 0; i < index; i++)
+            {
+                curr = curr.Next ?? throw new InvalidOperationException("Index exceeds list bounds.");
+            }
+
+            return curr.Value ?? throw new InvalidOperationException("Null value encountered at index.");
+        }
+        set => throw new NotImplementedException();
+    }
+
+    /// <inheritdoc/>
+    public IEnumerator<T> GetEnumerator()
+    {
+        var curr = this.baseHeader.Next;
+        var startVersion = this.currentVersion;
+        while (curr != this.sentinel && curr != null)
+        {
+            if (startVersion != this.currentVersion)
+            {
+                throw new InvalidOperationException("Collection modified during enumeration.");
+            }
+
+            yield return curr.Value ?? throw new NullReferenceException("Element value is null.");
+            curr = curr.Next;
+        }
+    }
+
+    /// <inheritdoc/>
+    IEnumerator IEnumerable.GetEnumerator() => this.GetEnumerator();
+
+    /// <inheritdoc/>
+    public void Add(T item)
+    {
+        ArgumentNullException.ThrowIfNull(item);
+        var level = this.GenerateRandomLevel();
+        var curr = this.header;
+        var updateNodes = new SkipListNode[level];
+        for (var i = 0; i <= MaxLevel - level; i++)
+        {
+            curr = curr.Down ?? curr;
+        }
+
+        for (var lvl = level - 1; lvl >= 0; lvl--)
+        {
+            while (curr != null && curr.Next != null && curr.Next != this.sentinel && curr.Next.Value != null &&
+                   curr.Next.Value.CompareTo(item) < 0)
+            {
+                curr = curr.Next;
+            }
+
+            updateNodes[lvl] = curr ?? throw new InvalidOperationException("Cannot add null to skip list.");
+            curr = curr.Down;
+        }
+
+        SkipListNode? lower = null;
+        for (var lvl = 0; lvl < level; lvl++)
+        {
+            var newNode = new SkipListNode(item, updateNodes[lvl].Next, lower);
+            updateNodes[lvl].Next = newNode;
+            lower = newNode;
+        }
+
+        this.Count++;
+        this.currentVersion++;
+    }
+
+    /// <inheritdoc/>
+    public void Clear()
+    {
+        this.baseHeader = new SkipListNode(default, this.sentinel, this.sentinel);
+        var curr = this.baseHeader;
+        for (var level = 1; level < MaxLevel; level++)
+        {
+            curr = new SkipListNode(default, this.sentinel, curr);
+        }
+
+        this.header = curr;
+        this.Count = 0;
+        this.currentVersion++;
+    }
+
+    /// <inheritdoc/>
+    public bool Contains(T item)
+    {
+        ArgumentNullException.ThrowIfNull(item);
+        var curr = this.header;
+        while (curr != null)
+        {
+            while (curr.Next != null && curr.Next != this.sentinel &&
+                   curr.Next.Value != null &&
+                   curr.Next.Value.CompareTo(item) < 0)
+            {
+                curr = curr.Next;
+            }
+
+            if (curr.Next != null && curr.Next != this.sentinel &&
+                curr.Next.Value != null &&
+                curr.Next.Value.CompareTo(item) == 0)
+            {
+                return true;
+            }
+
+            curr = curr.Down;
+        }
+
+        return false;
+    }
+
+    /// <inheritdoc/>
+    public void CopyTo(T[] array, int arrayIndex)
+    {
+        ArgumentNullException.ThrowIfNull(array);
+        if (arrayIndex < 0 || arrayIndex >= array.Length || arrayIndex + this.Count > array.Length)
+        {
+            throw new ArgumentOutOfRangeException(nameof(arrayIndex));
+        }
+
+        var curr = this.baseHeader.Next;
+        var idx = arrayIndex;
+        while (curr != this.sentinel && curr != null)
+        {
+            array[idx++] = curr.Value ?? throw new InvalidOperationException("Null element in list.");
+            curr = curr.Next;
+        }
+    }
+
+    /// <inheritdoc/>
+    public bool Remove(T item)
+    {
+        ArgumentNullException.ThrowIfNull(item);
+        var curr = this.header;
+        var removed = false;
+        while (curr != null)
+        {
+            while (curr.Next != null && curr.Next != this.sentinel &&
+                   curr.Next.Value != null &&
+                   curr.Next.Value.CompareTo(item) < 0)
+            {
+                curr = curr.Next;
+            }
+
+            if (curr.Next != null && curr.Next != this.sentinel &&
+                curr.Next.Value != null &&
+                curr.Next.Value.CompareTo(item) == 0)
+            {
+                curr.Next = curr.Next.Next;
+                removed = true;
+            }
+
+            curr = curr.Down;
+        }
+
+        if (removed)
+        {
+            this.Count--;
+            this.currentVersion++;
+        }
+
+        return removed;
+    }
+
+    /// <inheritdoc/>
+    public int IndexOf(T item)
+    {
+        ArgumentNullException.ThrowIfNull(item);
+        var idx = 0;
+        var curr = this.baseHeader.Next;
+        while (curr != null && curr != this.sentinel)
+        {
+            if (curr.Value != null && curr.Value.CompareTo(item) == 0)
+            {
+                return idx;
+            }
+
+            if (curr.Value != null && curr.Value.CompareTo(item) > 0)
+            {
+                return -1;
+            }
+
+            curr = curr.Next;
+            idx++;
+        }
+
+        return -1;
+    }
+
+    /// <inheritdoc/>
+    public void Insert(int index, T item)
+    {
+        throw new NotSupportedException("Insertion at specific index not supported in sorted skip list.");
+    }
+
+    /// <inheritdoc/>
+    public void RemoveAt(int index)
+    {
+        if (index < 0 || index >= this.Count)
+        {
+            throw new ArgumentOutOfRangeException(nameof(index));
+        }
+
+        var item = this[index];
+        this.Remove(item);
+    }
+
+    private int GenerateRandomLevel()
+    {
+        var lvl = 1;
+        while (this.random.NextDouble() < 0.5 && lvl < MaxLevel)
+        {
+            lvl++;
+        }
+
+        return lvl;
+    }
+
+    private class SkipListNode(T? value, SkipListNode? next, SkipListNode? down)
+    {
+        public T? Value { get; set; } = value;
+
+        public SkipListNode? Next { get; set; } = next;
+
+        public SkipListNode? Down { get; set; } = down;
+    }
+}

HW4/SkipList/SkipList.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <OutputType>Library</OutputType>
+        <TargetFramework>net9.0</TargetFramework>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <Nullable>enable</Nullable>
+        <GenerateDocumentationFile>true</GenerateDocumentationFile>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <PackageReference Include="StyleCop.Analyzers" Version="1.2.0-beta.556">
+            <PrivateAssets>all</PrivateAssets>
+            <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+        </PackageReference>
+    </ItemGroup>
+
+    <ItemGroup>
+        <AdditionalFiles Include="stylecop.json" />
+    </ItemGroup>
+
+</Project>

HW4/SkipList/SkipListException.cs

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+// <copyright file="SkipListException.cs" company="khusainovilas">
+// Copyright (c) khusainovilas. All rights reserved.
+// </copyright>
+namespace SkipList;
+
+/// <summary>
+/// Exception for empty skip list operations.
+/// </summary>
+public class SkipListException : Exception
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="SkipListException"/> class.
+    /// </summary>
+    /// <param name="message">The error message.</param>
+    public SkipListException(string message)
+        : base(message)
+    {
+    }
+}

HW4/SkipList/stylecop.json

@@ -0,0 +1,9 @@
+{
+  "$schema": "https://raw.githubusercontent.com/DotNetAnalyzers/StyleCopAnalyzers/master/StyleCop.Analyzers/StyleCop.Analyzers/Settings/stylecop.schema.json",
+  "settings": {
+    "documentationRules": {
+      "companyName": "khusainovilas",
+      "copyrightText": "Copyright (c) {companyName}. All rights reserved."
+    }
+  }
+}