c# - 两个字符的组合

Question

我将输入作为 int 并根据该输入我想要两个字符的组合， 例如 我将输入作为 2 并且我有两个字符 x 和 y 所以我想要这样的组合

    xx,yy,xy,yx

如果输入是3，我要

    xxx,xyy,xxy,xyx,yxx,yyy,yxy.yyx

等等，我已经尝试了下面的代码，

     int input1 = 4;
        Double totalpossibilities = Math.Pow(2, input1);
        string[] PArray = new string[Convert.ToInt16(totalpossibilities)];
        char[] chars = new char[] { 'x', 'y'};

        for (int i = 0; i < totalpossibilities; i++)
        {
            string possibility = "" ;
            for (int j = 0; j < input1; j++)
            {
                Random random = new Random();
                int r = random.Next(chars.Length);
                char randomChar = chars[r];
                possibility = possibility + randomChar;

            }
            if (PArray.Contains(possibility))
            {
                i--;
            }
            else
                PArray[i] = possibility;
        }

但是正如你所看到的，我使用的是随机函数，所以我需要很长时间才能完成，是否有任何不同的逻辑？

Answer 1

使用从 here 中逐字复制的笛卡尔积扩展方法的副本:

static IEnumerable<IEnumerable<T>> CartesianProduct<T>(this IEnumerable<IEnumerable<T>> sequences) 
{ 
  IEnumerable<IEnumerable<T>> emptyProduct = new[] { Enumerable.Empty<T>() }; 
  return sequences.Aggregate( 
    emptyProduct, 
    (accumulator, sequence) => 
      from accseq in accumulator 
      from item in sequence 
      select accseq.Concat(new[] {item})); 
}

然后在你的代码中你可以:

IEnumerable<char> possibleCharacters = "xy";//change to whatever
int numberOfDigits = 3;

var result = Enumerable.Repeat(possibleCharacters, numberOfDigits)
     .CartesianProduct()
     .Select(chars => new string(chars.ToArray()));

//display (or do whatever with) the results
foreach (var item in result)
{
    Console.WriteLine(item);
}