Add bag datastructure (#531)

Author: kamikkels

DataStructures.Tests/BagTests.cs

@@ -0,0 +1,153 @@
+using System.Collections.Generic;
+using System.Linq;
+using DataStructures.Bag;
+using FluentAssertions;
+using NUnit.Framework;
+
+namespace DataStructures.Tests;
+
+internal class BagTests
+{
+    [Test]
+    public void Add_ShouldIncreaseCount()
+    {
+        // Arrange & Act
+        var bag = new Bag<int>
+        {
+            1,
+            2,
+            1
+        };
+
+        // Assert
+        bag.Count.Should().Be(3);
+    }
+
+    [Test]
+    public void Add_ShouldHandleDuplicates()
+    {
+        // Arrange & Act
+        var bag = new Bag<string>
+        {
+            "apple",
+            "apple"
+        };
+
+        // Assert
+        bag.Count.Should().Be(2);
+        bag.Should().Contain("apple");
+    }
+
+    [Test]
+    public void Clear_ShouldEmptyTheBag()
+    {
+        // Arrange
+        var bag = new Bag<int>
+        {
+            1,
+            2
+        };
+
+        // Act
+        bag.Clear();
+
+        // Assert
+        bag.IsEmpty().Should().BeTrue();
+        bag.Count.Should().Be(0);
+    }
+
+    [Test]
+    public void IsEmpty_ShouldReturnTrueForEmptyBag()
+    {
+        // Arrange
+        var bag = new Bag<int>();
+
+        // Act & Assert
+        bag.IsEmpty().Should().BeTrue();
+    }
+
+    [Test]
+    public void IsEmpty_ShouldReturnFalseForNonEmptyBag()
+    {
+        // Arrange
+        var bag = new Bag<int>
+        {
+            1
+        };
+
+        // Act & Assert
+        bag.IsEmpty().Should().BeFalse();
+    }
+
+    [Test]
+    public void GetEnumerator_ShouldIterateAllItems()
+    {
+        // Arrange
+        var bag = new Bag<int>
+        {
+            1,
+            2,
+            1
+        };
+
+        // Act
+        var items = bag.ToList();
+
+        // Assert
+        items.Count.Should().Be(3);
+        items.Should().Contain(1);
+        items.Should().Contain(2);
+    }
+
+    [Test]
+    public void Count_ShouldReturnZeroForEmptyBag()
+    {
+        // Arrange
+        var bag = new Bag<int>();
+
+        // Act & Assert
+        bag.Count.Should().Be(0);
+    }
+
+    [Test]
+    public void Count_ShouldReturnCorrectCount()
+    {
+        // Arrange
+        var bag = new Bag<int>
+        {
+            1,
+            2,
+            1
+        };
+
+        // Act & Assert
+        bag.Count.Should().Be(3);
+    }
+
+    [Test]
+    public void IEnumerableGetEnumerator_YieldsAllItemsWithCorrectMultiplicity()
+    {
+        // Arrange
+        var bag = new Bag<string>
+        {
+            "apple",
+            "banana",
+            "apple"
+        };
+        var genericBag = bag as System.Collections.IEnumerable;
+
+        // Act
+        var enumerator = genericBag.GetEnumerator();
+        var items = new List<object>();
+        while (enumerator.MoveNext())
+        {
+            items.Add(enumerator.Current!);
+        }
+
+        // Assert
+        items.Count(i => (string)i == "apple").Should().Be(2);
+        items.Count(i => (string)i == "banana").Should().Be(1);
+        items.Count.Should().Be(3);
+        items.Should().BeEquivalentTo(["apple", "apple", "banana"]);
+    }
+}

DataStructures/Bag/Bag.cs

@@ -0,0 +1,106 @@
+using System.Collections;
+using System.Collections.Generic;
+
+namespace DataStructures.Bag;
+
+/// <summary>
+/// Implementation of a Bag (or multiset) data structure using a basic linked list.
+/// </summary>
+/// <remarks>
+/// A bag (or multiset, or mset) is a modification of the concept of a set that, unlike a set, allows for multiple instances for each of its elements.
+/// The number of instances given for each element is called the multiplicity of that element in the multiset.
+/// As a consequence, an infinite number of multisets exist that contain only elements a and b, but vary in the multiplicities of their elements.
+/// See https://en.wikipedia.org/wiki/Multiset for more information.
+/// </remarks>
+/// <typeparam name="T">Generic Type.</typeparam>
+public class Bag<T> : IEnumerable<T> where T : notnull
+{
+    private BagNode<T>? head;
+    private int totalCount;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="Bag{T}" /> class.
+    /// </summary>
+    public Bag()
+    {
+        head = null;
+        totalCount = 0;
+    }
+
+    /// <summary>
+    /// Adds an item to the bag. If the item already exists, increases its multiplicity.
+    /// </summary>
+    public void Add(T item)
+    {
+        // If the bag is empty, create the first node
+        if (head == null)
+        {
+            head = new BagNode<T>(item);
+            totalCount = 1;
+            return;
+        }
+
+        // Check if item already exists
+        var current = head;
+        BagNode<T>? previous = null;
+
+        while (current != null)
+        {
+            if (EqualityComparer<T>.Default.Equals(current.Item, item))
+            {
+                current.Multiplicity++;
+                totalCount++;
+                return;
+            }
+
+            previous = current;
+            current = current.Next;
+        }
+
+        previous!.Next = new BagNode<T>(item);
+        totalCount++;
+    }
+
+    /// <summary>
+    /// Clears the bag.
+    /// </summary>
+    public void Clear()
+    {
+        head = null;
+        totalCount = 0;
+    }
+
+    /// <summary>
+    /// Gets the number of items in the bag.
+    /// </summary>
+    public int Count => totalCount;
+
+    /// <summary>
+    /// Returns a boolean indicating whether the bag is empty.
+    /// </summary>
+    public bool IsEmpty() => head == null;
+
+    /// <summary>
+    /// Returns an enumerator that iterates through the bag.
+    /// </summary>
+    public IEnumerator<T> GetEnumerator()
+    {
+        var current = head;
+
+        while (current != null)
+        {
+            // Yield the item as many times as its multiplicity, pretending they are separate items
+            for (var i = 0; i < current.Multiplicity; i++)
+            {
+                yield return current.Item;
+            }
+
+            current = current.Next;
+        }
+    }
+
+    /// <summary>
+    /// Returns an enumerator that iterates through the bag.
+    /// </summary>
+    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
+}

DataStructures/Bag/BagNode.cs

@@ -0,0 +1,14 @@
+namespace DataStructures.Bag;
+
+/// <summary>
+/// Generic node class for Bag.
+/// </summary>
+/// <typeparam name="T">A type for node.</typeparam>
+public class BagNode<T>(T item)
+{
+    public T Item { get; } = item;
+
+    public int Multiplicity { get; set; } = 1;
+
+    public BagNode<T>? Next { get; set; }
+}

README.md

@@ -247,6 +247,7 @@ find more than one implementation for the same objective but using different alg
       * [Levenshtein Distance](./Algorithms/Problems/DynamicProgramming/LevenshteinDistance/LevenshteinDistance.cs)
 
 * [Data Structures](./DataStructures)
+  * [Bag](./DataStructures/Bag) 
   * [Bit Array](./DataStructures/BitArray.cs)
   * [Timeline](./DataStructures/Timeline.cs)
   * [Segment Trees](./DataStructures/SegmentTrees)