Generate a unique id

Question

I am a student at university and our task is to create a search engine  I am having difficulty generating a unique id to assign to each url when added into the frontier  I have attempted using the SHA-256 hashing algorithm as well as Guid  Here is the code that i used to implement the guid   public string generateID string url add        long i   1       foreach  byte b in Guid NewGuid   ToByteArray                  i      int b   1              string number   String Format   0 d9     DateTime Now Ticks   10    1000000000        return number

User · Answer

We can do something like this  string TransactionID    BTRF  DateTime Now Ticks ToString   Substring 0  10

User · Answer

Why not just use ToString   public string generateID         return Guid NewGuid   ToString  N        If you would like it to be based on a URL  you could simply do the following   public string generateID string sourceUrl        return string Format   0   1 N    sourceUrl  Guid NewGuid         If you want to hide the URL  you could use some form of SHA1 on the sourceURL  but I m not sure what that might achieve

User · Answer

If you want to use sha-256  guid would be faster  then you would need to do something like  SHA256 shaAlgorithm   new SHA256Managed    byte   shaDigest   shaAlgorithm ComputeHash ASCIIEncoding ASCII GetBytes url    return BitConverter ToString shaDigest     Of course  it doesn t have to ascii and it can be any other kind of hashing algorithm as well

User · Answer

Why can t we make a unique id as below   We can use DateTime Now Ticks and Guid NewGuid   ToString   to combine together and make a unique id   As the DateTime Now Ticks is added  we can find out the Date and Time in seconds at which the unique id is created   Please see the code   var ticks   DateTime Now Ticks  var guid   Guid NewGuid   ToString    var uniqueSessionId   ticks ToString     -   guid    guid created by combining ticks and guid  var datetime   new DateTime ticks    for checking purpose var datetimenow   DateTime Now       both these date times are different    We can even take the part of ticks in unique id and check for the date and time later for future reference

User · Answer

Why don t use GUID   Guid guid   Guid NewGuid    string str   guid ToString

User · Answer

This question seems to be answered  however for completeness  I would add another approach   You can use a unique ID number generator which is based on Twitter s Snowflake id generator  C  implementation can be found here   var id64Generator   new Id64Generator             public string generateID string sourceUrl        return string Format   0   1    sourceUrl  id64Generator GenerateId         Note that one of very nice features of that approach is possibility to have multiple generators on independent nodes  probably something useful for a search engine  generating real time  globally unique identifiers      node 0 var id64Generator   new Id64Generator 0       node 1 var id64Generator   new Id64Generator 1           node 10 var id64Generator   new Id64Generator 10

User · Answer

Here is a  YouTube-video-id  like id generator e g   UcBKmq2XE5a   StringBuilder builder   new StringBuilder    Enumerable     Range 65  26       Select e   gt    char e  ToString         Concat Enumerable Range 97  26  Select e   gt    char e  ToString          Concat Enumerable Range 0  10  Select e   gt  e ToString          OrderBy e   gt  Guid NewGuid         Take 11       ToList   ForEach e   gt  builder Append e    string id   builder ToString      It creates random ids of size 11 characters  You can increase decrease that as well  just change the parameter of Take method   0 001  duplicates in 100 million

[c#] Generate a unique id

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