Prepare to Coding Interview > Know Data Structures > Hash Table

public class HashTableSimpleImplementation
{
    /*
        * Simple implementation of HashTable
    */
    private LinkedList<string>[] _hashTable;

    private int _hashTableSezie = 10;

    public HashTableSimpleImplementation()
    {
        _hashTable = new LinkedList<string>[_hashTableSezie];

        Init();
    }

    private void Init()
    {
        for(int i=0; i < _hashTable.Length; i++)
        {
            _hashTable[i] = new LinkedList<string>();
        }
    }

    /// <summary>
    /// Adding value to the hash table
    /// 1. Compute the hash code
    /// 2. Map the hash code to the array index by hashCode % array.length
    /// 3. Put the value to the index
    /// </summary>
    /// <param name="value"></param>
    public int Add(string value)
    {
        var index = GetIndex(value);

        _hashTable[index].AddLast(value);

        return index;
    }

    /// <summary>
    /// 1. Compute the hash code
    /// 2. Map the hash code to the array index by hashCode % array.length
    /// 3. Go to the index and find the value if present
    /// </summary>
    /// <param name="value"></param>
    /// <returns></returns>
    public string? Get(string value)
    {
        var index = GetIndex(value);

        var list = _hashTable[index];

        foreach(var item in list)
        {
            if (item.Equals(value))
            {
                return value;
            }
        }

        return null;
    }

    private int GetIndex(string value)
    {
        var hashCode = GetHashCode(value);

        var index = hashCode % _hashTableSezie;

        return index;
    }

    /// <summary>
    /// This implementation of hash code returns different code
    /// for the same string value on each run of the application
    /// </summary>
    /// <param name="value"></param>
    /// <returns></returns>
    private int GetHashCode(string value)
    {
        var hashCode = value.GetHashCode();

        return hashCode > 0 ? hashCode : hashCode * -1;
    }
}