Congratulations, you have just been hired by Amazon ! They would like to automate their warehouses and are asking you to code the basic outline they will be using.
Automation in real-life There was automation far before computers were invented. For instance, John Kay invented the ﬂying shuttle (he received the patent for his invention in 1733) that enabled the automation of looms (used to weave cloths). This was one of the great contributors to the industrial revolution. Nowadays, automation is expanding very quickly. Some striking examples include an almost fully automated plant in the delivery industry in Tianjin (China), receptionists who are replaced with robots or screens or the treatment of information that is done by facebook, google etc (or the grading of this course). We won’t be discussing here the societal changes (both positive — automation of tedious or dangerous tasks — or negative — removal of jobs) that will come with these changes.
Structure of the code that is provided to you You have ﬁve ﬁles that are provided to you. There are four classes. First there are Box and its subclass UrgentBox. A Box has a unique identiﬁer, a height and a length. They also have two ﬁelds next and previous that will be useful to construct linked lists. A Shelf is where you store Boxes. A Shelf has a length and a height. You can only store a Box on a Shelf if it ﬁts the remaining space (in height and in length). Boxes are stored in a two-way linked list. Finally, a Warehouse contains an array of Shelf and two linked lists which correspond to Boxes and Urgentboxes that need to be shipped. We assume that a Warehouse contains at least one Shelf. The class Warehouse contains two methods print and printShipping that are useful to test your code. We have only provided a very scarce testing framework in Tester.java and you should expand it.
Sort storage The height ﬁeld is really important : you cannot put a box that is 10 high into a spot that is 5 high. But at the same time, you do not want to put a box that is 10 high onto a shelf that is 30 high if there is some space left on a shelf 15 high. To make it simpler to place a box on the
optimal shelf, you are ﬁrst going to organize (sort) the shelves by increasing order of height.
Question 1. Implement merge sort in Warehouse to sort all shelves by increasing order of height. You will have to code mergeSort (divide part of merge sort) and merge (merging part). You can refer yourself to the slides of lecture 9 for the detailed algorithm (be careful, the indices in an array start at 0 in java). You can assume that the maximal height of a Shelf is 1000.
For the other methods that you are going to implement, you can assume that storage is already sorted.
Add Boxes Your warehouse is now ready ! You are starting to get boxes. You need to put them on the shelves : each box on its optimal shelf. This is what you are going to code now : ﬁrst how to add a box on a shelf and second decide which shelf from the warehouse to put the box onto (and do it).
Question 2. Implement addBox in Shelf. Here you can assume that the box given in argument ﬁts both in height and length so you don’t need to check it in this function. You will have to add it to the last position on the Shelf.
Question 3. Implement addBox in Warehouse : ﬁnd the smallest shelf with enough space available for the box given in argument, add the box on this shelf and return the noProblem message. If there is no such shelf, do not do anything to the warehouse and return the problem message.
Shipping Boxes Ultimately, you want to send to each customer what he ordered from Amazon. You are going to implement this part now. First, you are going to implement the method that removes a box from the shelf it was on, then you are going to implement an auxiliary method that puts a box into the appropriate shipping list and ﬁnally you are going to implement the method that ﬁnds the box with a given id, removes it from its shelf and put it into the corresponding shipping list.
Question 4. Implement removeBox in Shelf. The argument is the id String of a box. If you can ﬁnd a Box with that identifier, remove it from the Shelf and return the box you have found. Do not forget to update all the ﬁelds that need to be. If there is no Box on that Shelf, return null.
Question 5. Implement addToShip in Warehouse. The argument given is a Box. If that box is an Urgentbox, it is added to the beginning of the
toShipUrgently list. Otherwise it is added to the beginning of the toShip list. Do not forget to update all the ﬁelds that need to be. The method returns noProblem if everything was done successfully, problem otherwise.
The method addToShip is an auxiliary method for the method shipBox that you will code next.
Question 6. Implement shipBox in Warehouse. The argument given is the identiﬁer of a Box. If a Box with such identiﬁer exists, remove it from its corresponding Shelf and add it to its corresponding shipping list, then return noProblem. If no such Box exists in the entire warehouse, return Problem.
Moving Boxes around Your warehouse is now fully functional : each day you receive and ship boxes. But the placement of the boxes may become non optimal. Let us see why on an example : there are two shelves with height 15 and 20 respectively and length 10 for both. You receive a ﬁrst box of height 15 and length 10. You place it on the ﬁrst shelf (of height 15). You now receive a second box of height 15 and length 10, so you place it on the second shelf. And then you ship the ﬁrst box. So the ﬁrst shelf is empty and the second shelf has the box of height 15. Now if you receive a third box of height 16, you have to send it back saying “sorry, no room left”. But if you had moved the second box on the ﬁrst shelf, you could have stored the third box on the last shelf ! You are going to implement this reorganization of the warehouse, ﬁrst for a single box, then for the entire warehouse.
Question 7. Implement moveOneBox in Warehouse. The arguments are a Box and a number of Shelf corresponding to the Shelf on which the Box sits. If there is a Shelf with a smaller height where the Box would ﬁt, move the Box to the end of that new Shelf (and don’t forget to update all the ﬁelds that need to be)
Question 8. Implement reorganize in Warehouse. Start with the lower Shelf and the ﬁrst Box on this Shelf and go on until the last Box on the last Shelf. You can optimize this procedure, but this is the order we are looking for.