Question

我正在尝试在C＃中创建一个随机字符串生成器，给定字符串的长度。我的第一次尝试是这样的：

public static string RandomString(int characters)
{
    string s = "";
    for (int i = 0; i < characters; i++)
    {
        s += Convert.ToChar((97 + r.Next(26)));
    }
    return s;
}

但是 k 之前字母的频率非常低，所以我试着通过编写自己的随机函数来改变它：

public static string RandomString(int characters)
{
    string s = "";
    for (int i = 0; i < characters; i++)
    {
        int randomLetter = 0;

        for (int bit = 0; i < 5; bit++)
        {
            if (r.Next(2) == 0)
                continue;
            randomLetter += 1 << bit;

            if (randomLetter + (1 << (bit + 1)) > 26)
                break;
        }
        s += Convert.ToChar(97 + randomLetter);
    }
    return s;
}

但有时randomLetter会大于26，有时候太大了。我找不到这个问题的原因，可以吗？

Answer 1

如果您只想要一个简单的随机字符串，这种方法应该更简单：

private static Random random = new Random();

public static string GetRandomString(int length)
{
    var chars = new char[length];
    var possibleLetters = "abcdefghijklmnopqrstuvwxyz";        

    for (int i = 0; i < length; i++)
    {
        chars[i] = possibleLetters[random.Next(0, possibleLetters.Length - 1)];
    }

    return new string(chars);
}

我刚用你的代码对我的控制台进行了测试：

System.Diagnostics.Stopwatch sw = new System.Diagnostics.Stopwatch();
sw.Start();
for (int i = 0; i < 1000; i++)
{
   string s = RandomString(10000);
}
sw.Stop();
Console.WriteLine(sw.Elapsed.TotalMilliseconds);
sw.Restart();

for (int i = 0; i < 1000; i++)
{
    string s = GetRandomString(10000);
}

sw.Stop();
Console.WriteLine(sw.Elapsed.TotalMilliseconds);
Console.Read();

结果：

RandomString => 18830,7537
GetRandomString => 321.098

正如您所看到的，您的实现不仅更糟糕，而且执行速度也慢得多。

为了证明好奇心，我用StringBuilder重新创建了我的方法：

private static string GetRandomStringSB(int length)
{
   var stringBuilder = new StringBuilder(length);

   var possibleLetters = "abcdefghijklmnopqrstuvwxyz";

   for (int i = 0; i < length; i++)
   {
       stringBuilder.Append(possibleLetters[r.Next(0, possibleLetters.Length - 1)]);
   }

   return stringBuilder.ToString();
}

毫不奇怪，结果并没有太多推迟：

RandomString (OP) => 13175
GetRandomString (char[]) => 213
GetRandomStringSB (StringBuilder) => 244

Answer 2

为什么所有这些按位算术？首先，让我们说明问题：

我想生成characters长度的随机字符串;该字符串应包含a .. z 应该有均匀分布

实施起来很简单：

// Simplest, but not thread safe
private static Random s_Random = new Random();

// Not thread safe
public static string RandomString(int characters) {
  if (characters < 0)
    throw new ArgumentOutOfRangeException("characters");

  StringBuilder sb = new StringBuilder(characters);

  // I personally, prefer Linq + Concat, but let's preserve the loop
  for (int i = 0; i < characters; ++i) {
    char c = (char)(s_Random.Next('z' - 'a' + 1) + 'a'); // +1 - 'z' should be included

    sb.Append(c);
  }

  return sb.ToString();
}

Linq 版本更短，但可能更少可读：

// Not thread safe
public static string RandomString(int characters) {
  if (characters < 0)
    throw new ArgumentOutOfRangeException("characters");

  return string.Concat(Enumerable
    .Range(0, characters)
    .Select(i => (char)(s_Random.Next('z' - 'a' + 1) + 'a')));
}

测试：

Console.Write(RandomString(10));

结果（可能会有所不同）：

dcdwwvzhnz

最后，让我们看一下实际的发布＆＃34; ...但的频率之前 strong> k 非常低 ..＆＃34;

int count = 1000; // we examine "count" random string int length = 10; // each of "length" length var distribution = String .Concat(Enumerable.Range(1, count).Select(i => RandomString(length))) .GroupBy(c => c, (k, s) => new { key = k, freq = (double)s.Count() / length / count }) .OrderBy(item => item.freq) .Select(item => $"{item.key}: {item.freq:F4}") .ToArray(); Console.Write(string.Join(Environment.NewLine, distribution));

结果（可能会有所不同）：没有证据这样的倾斜

p: 0.0351 a: 0.0359 r: 0.0360 y: 0.0362 l: 0.0363 z: 0.0364 n: 0.0369 u: 0.0370 h: 0.0371 e: 0.0373 c: 0.0375 v: 0.0376 x: 0.0376 o: 0.0380 q: 0.0380 m: 0.0388 k: 0.0389 d: 0.0391 s: 0.0391 g: 0.0396 w: 0.0401 b: 0.0406 t: 0.0406 f: 0.0422 i: 0.0434 j: 0.0447

Answer 3

使用这些方法，您可以指定有效字符，或接受所有字符。

    public static string RandomString(int len)
    {
        var array = Enumerable.Range(char.MinValue, char.MaxValue - char.MinValue + 1).Select(x => (char)x).ToArray();
        return RandomString(len, array);
    }

    private static string RandomString(int len, char[] array)
    {
        Random r = new Random();
        StringBuilder sb = new StringBuilder();
        while (sb.Length < len)
            sb.Append(array[r.Next(array.Length-1)]);
        return sb.ToString();
    }

Answer 4

这是一个简单的函数，可以生成随机字符串

.once()

Answer 5

如果你想随机。

private static System.Security.Cryptography.RandomNumberGenerator random = System.Security.Cryptography.RandomNumberGenerator.Create();
public static string Random(int characters)
        {
            var data = new byte[characters];
            random.GetBytes(data);
            return data.Select(b=>Convert.ToChar((int)(96 + (Math.Floor((b/(double)byte.MaxValue)*27)) - 1))).Aggregate(new System.Text.StringBuilder(),(a,c) => a.Append(c)).ToString();
        }

请注意，这不是快速而是随机的

Answer 6

感谢@Evk我明白了。我最后的方法：

public static string RandomString(int characters)
    {
        string s = "";
        for (int i = 0; i < characters; i++)
        {
            int ascii = 0;

            for (int bit = 0; bit < 5; bit++)
            {
                if (r.Next(2) == 0)
                    continue;
                ascii += 1 << bit;

                if (ascii + (1 << (bit + 1)) > 25)
                    break;
            }
            s += Convert.ToChar(97 + ascii);
        }
        return s;
    }

随机字符串生成器：Unicode超出范围？

6 个答案: