SeparateChainingHashTable.cs

using System;
using System.Collections.Generic;
using System.Linq;

namespace AlgorithmsAndDataStructures.DataStructures.HashTable;

public class SeparateChainingHashTable<TKey, TValue>
{
    private readonly LinkedList<HashEntry<TKey, TValue>>[] hashTable;

    public SeparateChainingHashTable(int hashTableSize = 8)
    {
        hashTable = new LinkedList<HashEntry<TKey, TValue>>[hashTableSize];
    }

    public void Add(TKey key, TValue value)
    {
        var hash = Math.Abs(key.GetHashCode() % hashTable.Length);

        hashTable[hash] ??= new LinkedList<HashEntry<TKey, TValue>>();

        var entry = hashTable[hash]?.FirstOrDefault(arg => arg.Key?.Equals(key) == true);

        if (entry != null)
            entry.Value = value;
        else
            hashTable[hash].AddLast(new HashEntry<TKey, TValue> { Value = value, Key = key });
    }

    public bool Find(TKey key)
    {
        var hash = Math.Abs(key.GetHashCode() % hashTable.Length);

        return hashTable[hash]?.FirstOrDefault(arg => arg.Key?.Equals(key) == true) != null;
    }

    public TValue Get(TKey key)
    {
        var hash = Math.Abs(key.GetHashCode() % hashTable.Length);

        var entry = hashTable[hash]?.FirstOrDefault(arg => arg.Key?.Equals(key) == true);

        if (entry is null) throw new ArgumentException($"Hash table contains no entry with key {key}");

        return entry.Value;
    }

    public void Delete(TKey key)
    {
        var hash = Math.Abs(key.GetHashCode() % hashTable.Length);

        var entry = hashTable[hash]?.FirstOrDefault(arg => arg.Key?.Equals(key) == true);

        if (entry != null) hashTable[hash].Remove(entry);
    }
}