Simple permutation algorithm

Question

I’m trying to create a simple permutation algorithm where you pass any number for example 123 and it should return the largest number without repeating. I tried something like this more when I pass 4242 it does not return me 4422 and yes 4242 as higher.

 static void ComparacoesPossiveis(ref int entrada, out int saida)
        {
            saida = 1;
            for (int i = 1; i <= entrada; i++)
            {
                saida *= i;
            }
        }

        public static void teste(int number)
        {
            if (number >= 10000000)
            {
                Console.WriteLine(-1);
                Console.ReadKey();
                return;
            }

            var array = number.ToString().ToArray();

            int tamanhoArray = array.Length;
            int[] vetor = new int[tamanhoArray];
            int[] temp = new int[tamanhoArray];
            int[] vetTmp = new int[tamanhoArray];

            for (int i = 0; i < tamanhoArray; i++)
            {
                vetor[i] = Convert.ToInt32(array[i].ToString());
            }

            int y, x;
            y = vetor.Length;
            ArrayList combinacoes = new ArrayList();

            ComparacoesPossiveis(ref y, out x);

            while (x > 0)
            {
                for (int j = 0; j < y - 1; j++)
                {

                    string numero = "";

                    vetTmp[j] = vetor[j];
                    vetor[j] = vetor[j + 1];
                    vetor[j + 1] = vetTmp[j];


                    for (int i = 0; i < vetor.Length; i++)
                        numero += vetor[i].ToString();

                    combinacoes.Add(Convert.ToInt32(numero));
                }
                x -= y;
            }

            combinacoes.Sort();

            Console.WriteLine("O maior numero é " + combinacoes[combinacoes.Count - 1].ToString());
            Console.ReadKey();
        }

Answer 1

Since you are using modernities and ready-made functions that do the work for you, there is no need to complicate so much:

public static int Teste(int number) => number >= 10000000 ? -1 : ToInt32(new string(number.ToString().OrderByDescending(x => x).ToArray()));

Behold working in the ideone. And in the .NET Fiddle. Also put on the Github for future reference.

Note that I have separated the processing from the presentation, so it is more organized.

If you were to use the original code you would have to fix the error, but the error occurred because the code was too complicated. As it was simplifying it would be easy to find the error, or the simplification would already eliminate the error.

I point out that that code had several inconsistencies and used a non-indigmatic pattern for C#. It would be easy to eliminate the ref and mainly out in auxiliary function.

I wouldn’t need to create a list to generate the highest number, but if I had to, I would List<char> and not a ArrayList that should no longer be used in any code.

There are too many variables in the code, duplicating the data from one variable to another without any need, meaningless links.

If I were to use a manual algorithm, I would start doing one from scratch in a simpler way.