// ISO 6346

// does NOT validate the "Check Digit"

private static Regex containerNumberRegex = new Regex("^[a-zA-Z]{3}[uUjJzZ]{1}[0-9]{7}$");
public static bool IsValidContainerNumber(string text) => containerNumberRegex.IsMatch(text);


IsValidContainerNumber(" MEDU8707688  ".Trim())



//////////////////////////////
// Code to get Check digit
//////////////////////////////

private static string CharacterValues = "0123456789A_BCDEFGHIJK_LMNOPQRSTU_VWXYZ"; // skip 11th values

// short Linq version
private static int GetCheckDigit(string containerNumber) 
{
    var sum = containerNumber.Select((c, i) => CharacterValues.IndexOf(c) * Math.Pow(2, i)).Sum();
    return (int)(sum - (Math.Floor(sum / 11.0) * 11.0));
}

// comprehensive version
private static int GetCheckDigit(string containerNumber) 
{
    var sum = 0.0;
    for (int i = 0; i < containerNumber.Count(); i++)
    {
        char c = containerNumber[i];
        var power = Math.Pow(2, i);
		var charValue = CharacterValues.IndexOf(c);
		Console.WriteLine($"{i}: [{c}] {power,4} * {charValue,4} = {power*charValue,4}");
        sum += CharacterValues.IndexOf(c) * power;
    }
    var rest =  Math.Floor(sum / 11.0) * 11.0;
	Console.WriteLine($"sum-rest: {sum} - {rest} = {sum - rest}");
    return (int)Math.Floor(sum - rest);
}

void Main()
{
	Console.WriteLine(GetCheckDigit("CSQU305438"));
}


/* OUTPUT:
0: [C]    1 *   13 =   13
1: [S]    2 *   30 =   60
2: [Q]    4 *   28 =  112
3: [U]    8 *   32 =  256
4: [3]   16 *    3 =   48
5: [0]   32 *    0 =    0
6: [5]   64 *    5 =  320
7: [4]  128 *    4 =  512
8: [3]  256 *    3 =  768
9: [8]  512 *    8 = 4096
sum-rest: 6185 - 6182 = 3
3
*/