Write a backend server that takes a two dimensional array and gives each cell a character - the cells are basically shelves in a storage and you need to find the shelf with the right characteristic to the corresponding product. For example you get a delivery of 5 units of milk and you need to find a shelf (a cell in the array) that had 5 free spots (each cell has 10 spots) and that it also has the character of refrigeration. The challenge was to easily allow extension of the existing characteristics of the two dimensional array (the storage) while finishing it all and making it work with a very short time frame.