Excel Kata

Excel column encoding and decoding problem used in coding challenge

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Excel Coding Challenge

In this coding challenge, you will exercise your basic algorithmic skills, your ability to setup a basic webapp and your ability to interact with an external API.


You know how the columns in spreadsheets are identified by letters? They start with A and go through to Z. And what’s the column identifier after Z? AA, then AB and so on.


The coding challenge is to write two functions. The first will take a positive integer greater than or equal to 1 and return the corresponding spreadsheet column notation. The second will take a string of letters and convert those letters to the corresponding column number.


toColNotation(1)        ->  A
toColNotation(27)       ->  AA
toColNotation(731)      ->  ABC

fromColNotation("A")    ->  1
fromColNotation("AA")   ->  27
fromColNotation("ABC")  ->  731


To verify the results of your functions, there are two endpoints at your disposal:



curl https://code-challenge.afitnerd.com/v1/excel_kata/to_col_notation/1
-> {"result":"A"}

curl https://code-challenge.afitnerd.com/v1/excel_kata/from_col_notation/A
-> {"result":1}

App Requirements

  1. We should be able to run your code and query your server with:
    • http://localhost:<port>/code_challenge/to_col_notation/:num
    • http://localhost:<port>/code_challenge/from_col_notation/:str
  2. Must communicate with the https://code-challenge.afitnerd.com server to verify your algorithm
  3. Send over your code and some brief instructions so we can get it up and running locally
  4. Send us your code or a link to your repo at: [email protected]