Convert AlphaNumeric To Numeric And Should Be An Unique Number

Question

I want to convert an alphanumeric(string) value to numeric(int). alphanumeric values like 'af45TR'. I wanted that numeric(int) value should be unique and it should not go out of the size of int like 64, 32 bits. How can i do that?.

Answer 1

If you consider the string to be a number in base 62, you could write a function to perform a base conversion from base 62 to base 10. An example in PHP could be;

function base62toDec($n)
{
    $vals = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
    $vals = array_flip(str_split($vals));
    $out = 0;
    $len = strlen($n);
    for ($i = 0; $i < $len; $i++) {
        $c = $n[$len - ($i + 1)];
        $out += $vals[$c] * pow(62, $i);
    }
    return $out;
}

echo base62toDec('af45TR'); // outputs 9383949355

Answer 2

You can map but for all alphanumeric you cannot have a unique numeric. just use pigeon hole principle you have larger space for alphanumeric but comparatively small space for numeric.

so first specify max length of you string then some algorithm can easily be devised. Use hash based algorithm they have very low probability of having same hash value and can be specified to just return digits only in hash.

I hope it helps.

Answer 3

I had to implement going from string to decimal and back again. Thanks to @Pudge601 for the base 62 idea. Please find below a C# solution.

Limitations: Using long data type, appears to only handle 10 characters or less at base 62. Using int32, appears to only handle 5 characters at worst case - so it doesn't handle your example 'af45TR' string.

readonly char[] charArray = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ".ToCharArray();
void Main()
{   
    var stringToConvert = "HelloWorld";
    var decimalVal = StringToDecimal(stringToConvert, 62); // outputs 598985658527080986 
    var result = DecimalToString(decimalVal, 62, stringToConvert.Length);
    Console.WriteLine(result); // outputs HelloWorld
}

public string DecimalToString(long decimalInput, int desiredBased, int expectedStringLength) 
{ 
    Console.WriteLine($"Converting decimal value {decimalInput} to string using base {desiredBased}");
    var index = 0;  // Initialize index of result 
    var output = new char[expectedStringLength];
    while (decimalInput > 0) 
    {       
        var deciValue = (decimalInput % desiredBased);
        if (deciValue == 0) // handle Z value
            deciValue = 62;
        output[index] = charArray[deciValue-1];
        index ++;
        decimalInput = (decimalInput - deciValue) / desiredBased;
    } 
    // Reverse the result 
    Array.Reverse(output);

    return new string(output);   
} 

public long StringToDecimal(string input, int desiredBase) 
{       
    Console.WriteLine($"Converting string value {input} to decimal using base {desiredBase}");
    int len = input.Length; 
    long power = 1;
    long num = 0;  
    for (var i = len - 1; i >= 0; i--) 
    {
        if (Array.IndexOf(charArray, input[i]) + 1 > desiredBase) 
        { 
            throw new ArgumentException("Invalid base", nameof(desiredBase));
        } 
        num += (Array.IndexOf(charArray, input[i]) + 1) * power; 
        power = power * desiredBase; 
    }   
    return num; 
} 

With help from geeksforgeeks, although their solution did not work straight out of the box for me.