TopKFrequent

TopKFrequent.cs

public static int[] TopKFrequent(int[] nums, int k)
{
    //By bucket sort
    if (nums.Length == 0 || k == 0)
        return Array.Empty();

    var result = new List();
    Dictionary num2count = new Dictionary();
    foreach (var item in nums)
    {
        if (num2count.ContainsKey(item))
            num2count[item]++;
        else
            num2count.Add(item, 1);
    }

    List[] bucket = new List[nums.Length + 1];
    foreach (var key in num2count.Keys)
    {
        int frequent = num2count[key];
        if (bucket[frequent] == null)
        {
            bucket[frequent] = new List();
        }

        bucket[frequent].Add(key);
    }

    for (var i = bucket.Length - 1; i > 0; i--)
    {
        if (bucket[i] != null)
        {
            foreach (var item in bucket[i])
            {
                result.Add(item);
                if (result.Count == k)
                    return result.ToArray();
            }
        }
    }

    return result.ToArray();
}