using System;

using System.Linq;

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

public class Program

{

    public static void Main()

    {

        string json = @"

        {

          ""keyXXX"": [[1, 2, 3]],

          ""last"": 12345

        }";

        DPInfo info = JsonConvert.DeserializeObject<DPInfo>(json);

​

        Console.WriteLine("key: " + info.key);

        Console.WriteLine("points: " + string.Join(", ", info.points[0].Select(x => x.ToString())));

        Console.WriteLine("last: " + info.last);

    }

}

​

public class DPInfoConverter : JsonConverter

{

    public override bool CanConvert(Type objectType)

    {

        return objectType == typeof(DPInfo);

    }

​

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)

    {

        JObject obj = JObject.Load(reader);

        JProperty points = obj.Properties().FirstOrDefault(p => p.Name != "last");

​

        DPInfo info = new DPInfo

        {

            key = points.Name,   // remove this line if you don't need the key

            points = points.Value.ToObject<decimal[][]>(),

            last = (long)obj["last"]

        };

​

        return info;

    }

​

    public override bool CanWrite

    {

        get { return false; }

    }

​

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)

    {

        throw new NotImplementedException();

    }

}

​

[JsonConverter(typeof(DPInfoConverter))]

public class DPInfo

{

    public string key { get; set; }   // remove this line if you don't need the key

    public decimal[][] points { get; set; }

    public long last { get; set; }

}