/SimpleDatabase

Thumbtack's Simple Database Challenge

Primary LanguageJava

Simple Database Challenge

In the Simple Database problem, you'll implement an in-memory database similar to Redis. For simplicity's sake, instead of dealing with multiple clients and communicating over the network, your program will receive commands via standard input (stdin), and should write appropriate responses to standard output (stdout).

Guidelines

  • We recommend that you use a high-level language, like Python, Go, Haskell, Ruby, or Java. We're much more interested in seeing clean code and good algorithmic performance than raw throughput.
  • It is very helpful to the engineers who grade these challenges if you reduce external dependencies, make compiling your code as simple as possible, and include instructions for compiling and/or running your code directly from the command line, without the use of an IDE.
  • Your submission must comply with the input/output formats and performance requirements specified below.

Data Commands

Your database should accept the following commands:

  • SET name value – Set the variable name to the value value. Neither variable names nor values will contain spaces.
  • GET name – Print out the value of the variable name, or NULL if that variable is not set.
  • UNSET name – Unset the variable name, making it just like that variable was never set.
  • NUMEQUALTO value – Print out the number of variables that are currently set to value. If no variables equal that value, print 0.
  • END – Exit the program. Your program will always receive this as its last command.

Commands will be fed to your program one at a time, with each command on its own line. Any output that your program generates should end with a newline character. Here are some example command sequences:

INPUT             OUTPUT
SET ex 10
GET ex            10
UNSET ex
GET ex            NULL
END

INPUT             OUTPUT
SET a 10
SET b 10
NUMEQUALTO 10     2
NUMEQUALTO 20     0
SET b 30
NUMEQUALTO 10     1
END

Transaction Commands

In addition to the above data commands, your program should also support database transactions by also implementing these commands:

  • BEGIN – Open a new transaction block. Transaction blocks can be nested; a BEGIN can be issued inside of an existing block.
  • ROLLBACK – Undo all of the commands issued in the most recent transaction block, and close the block. Print nothing if successful, or print NO TRANSACTION if no transaction is in progress.
  • COMMIT – Close all open transaction blocks, permanently applying the changes made in them. Print nothing if successful, or print NO TRANSACTION if no transaction is in progress.

Any data command that is run outside of a transaction block should commit immediately. Here are some example command sequences:

INPUT             OUTPUT
BEGIN
SET a 10
GET a             10
BEGIN
SET a 20
GET a             20
ROLLBACK
GET a             10
ROLLBACK
GET a             NULL
END

More details on this challenge can be found on thumbtack's page - link.