Key 값의 갯수를 포함하는 간단한 Dictionary입니다.

CountDictionary.cs

public class CountDictionary<TKey> : IDictionary<TKey, int> where TKey : notnull
{
    public CountDictionary()
    {
        Collections = new();
    }
    public CountDictionary(IEnumerable<KeyValuePair<TKey, int>> pair)
    {
        Collections = new(pair);
    }
    private Dictionary<TKey, int> Collections { get; init; }
    public int this[TKey key] { get => Collections[key]; set => Collections[key] = value; }
    public ICollection<TKey> Keys => Collections.Keys;
    public ICollection<int> Values => Collections.Values;
    public int Count => Keys.Count;
    public bool IsReadOnly => false;
    public void Add(TKey key, int value)
    {
        if (Collections.ContainsKey(key))
            Collections[key] += value;
        else
            Collections.Add(key, value);
    }
    public void Add(TKey key)
        => Add(key, 1);
    public void Sub(TKey key, int value)
    {
        if (Collections.ContainsKey(key))
            Collections[key] -= value;
        else
            throw new KeyNotFoundException();
    }
    public void Sub(TKey key)
        => Sub(key, 1);
    public void Add(KeyValuePair<TKey, int> item)
        => Add(item.Key, item.Value);
    public void Clear()
        => Collections.Clear();
    public bool Contains(KeyValuePair<TKey, int> item)
        => Collections.Contains(item);
    public bool ContainsKey(TKey key)
        => Collections.ContainsKey(key);
    public void CopyTo(KeyValuePair<TKey, int>[] array, int arrayIndex)
        => new NotImplementedException();
    public IEnumerator<KeyValuePair<TKey, int>> GetEnumerator()
        => Collections.GetEnumerator();
    public bool Remove(TKey key)
        => Collections.Remove(key);
    public bool Remove(KeyValuePair<TKey, int> item)
        => Collections.Remove(item.Key);
    public bool TryGetValue(TKey key, [MaybeNullWhen(false)] out int value)
    {
        if (Collections.TryGetValue(key, out int values))
        {
            value = values;
            return true;
        }
        value = default;
        return false;
    }
    IEnumerator IEnumerable.GetEnumerator()
        => Collections.GetEnumerator();
}