从不使用 .GetHashCode() 的唯一字符串生成短整数

Question

I'd like to generate a short integer when given a unique string. Note the string will never be more than 3 characters long, only alpha characters, can be either upper or lower case. For instance, AB should not return the same value as BA . I tried something like the following (below), only to run into BA being equal to AK :

public static class StringExtensions
{
    public static int StringToASCIIValue(this string str)
    {
        if (string.IsNullOrWhiteSpace(str)) 
            throw new ArgumentException("string must not be null or whitespace");

        int result = 0;
        foreach (char singleChar in str)
        {
            result = 10 * result + singleChar - '0';
        }
        return result;
    }
}

Answer 1

Here is a simple way to accomplish this. No two results will be the same. We take the string, then for each character in it we append the ascii value to a string builder. When we are done we can output a unique integer for that character combination.

string first = "AB";
StringBuilder stringBuilder = new StringBuilder();

foreach(char c in first)
{
     stringBuilder.Append((int)c);
}

Console.WriteLine(stringBuilder.ToString());

Output

6566

Answer 2

If you're really sure you're not ever looking at more than 3 alphabetic ( AZ or az ) characters, you should be able to just get the ASCII encoded bytes and convert them directly to an int .

public static class StringExtensions
{
    public static int ToInt32(this string str)
    {
        // Checks for null omitted.
        var ascii = System.Text.Encoding.ASCII.GetBytes(str);
        int result = 0;
        for (int i = 0; i < ascii.Length; i++)
        {
            result = result | (ascii[i] << (i * 8));
        }
        return result;
    }
}

If it matters, you can then take that int back to the string that generated it.

public static class StringExtensions
{   
    public static string AsciiIntBackToString(this int value)
    {
        var bytes = BitConverter
            .GetBytes(value)
            .Where(b => b > 0)
            .ToArray();
        return System.Text.Encoding.ASCII.GetString(bytes);
    }
}