using System;

public class Program

{

    public static void Main()

    {

        string mat = "[[1,2,3],[4,5,6]]";

        string[] arr = mat.Split('[', ']');

​

        foreach (string algo in arr){

            if (string.IsNullOrWhiteSpace(algo)) continue;

            Console.WriteLine(algo.Trim());

            string[] arr2 = algo.Split(',');

            foreach (string algo2 in arr2){

                if (string.IsNullOrWhiteSpace(algo2)) continue;

                int valor = 0;

                if (!int.TryParse(algo2, out valor)) continue;

                Console.WriteLine(algo2.Trim() + ": " + valor);

            }

        }

    }

}