C#方法从List <T>中删除重复项

public static List<T> RemoveDuplicates<T>(List<T> list)
{
    HashSet<T> set = new HashSet<T>(list);
    return set.ToList();
}

using System.Linq;

public static List<T> RemoveDuplicates<T>(List<T> list)
{
    return list.Distinct().ToList();
}

public static List<T> RemoveDuplicates<T>(List<T> list)
{
    for (int i = 0; i< list.Count; i++)
    {
        for (int j = i + 1; j< list.Count; j++)
        {
            if (list[i].Equals(list[j]))
            {
                list.RemoveAt(j);
                j--;
            }
        }
    }
    return list;
}

public static List<T> RemoveDuplicates<T>(List<T> list)
{
    Dictionary<T, bool> dict = new Dictionary<T, bool>();
    List<T> result = new List<T>();

    foreach (T item in list)
    {
        if (!dict.ContainsKey(item))
        {
            dict.Add(item, true);
            result.Add(item);
        }
    }

    return result;
}