I have had the displeasure of being saddled with a textbook that isn't written very well. As it stands, I went from enjoying C++ to being physically ill just thinking about it. However, I refuse to quit the class. So the long and short of it is I have a lab that asks the following:
Write a program that contains two arrays called actors and roles, each of size N. For each i, actors[i] is the name of an actor and roles[i] is a multiset of strings that contains the names of the movies that the actor has appeared in. The program reads the initial information for the these arrays from files in a format that you design. Once the program is running, the user can type in the name of an actor and receive a list of all the movies for that actor. Or the user may type the name of a movie and receive a list of all the actors in that movie.
Now, I don't want the answer. I just need to know what direction to start heading to. I feel pretty comfortable with standard arrays, but the way multisets are described in this textbook confuses me to no end. Any assistance (without just giving me the answer) would be appreciated.
The way its done is to have a third auxiliary multiset linking actors to films.
This third set only needs to contain pairs of unique integers. Say user picks actor 'wayne' first step is to form auxiliary subset of pairs of integers(actor_id,movie_id),each actor has an unique integer id, each movie has an unique integer id , then iterate through this set to obtain all movies as values to these keys.
Going the other way: if user picks film 'rawhide' again form subset of integers and iterate through this to find all actors as values to these keys.
Look up 'many to many relation' for further info.
Related
basically my whole career is based on reading question here but now I'm stuck since I even do not know how to ask this correctly.
I'm designing a SQLITE database which is meant for the construction of data sheets out of existing data sheets. People like reusing stuff and I want to manage this with a DB and an interface. A data sheet has reusable elements like pictures, text, formulas, sections, lists, frontpages and variables. Sections can contain elements -> This can be coped with recursive CTEs - thanks "mu is too short" for that hint. Texts, Formulas, lists etc. can contain variables. At the end I want to be able to manage variables which must be unique per data sheet, manage elements which are an ordered list making up the data sheet. So selecting a data sheet I must know which elements are contained and what variables within the elements are used. I must be able to create a new data sheet by re-using elements and/or creating new ones if desired.
I came so far to have (see also link to screen shot at the bottom)
a list of variables
which (several of them) can be contained in elements
a list of elements
elements make up the
a list of data sheets
Reading examples like
Store array in SQLite that is referenced in another table
How to store a list in a column of a database table
give me already helpful hints like that I need to create for each data sheet a new atomic list containing the elements and the position of them. Same for the variables which are referenced by each element. But the troubles start when I want to have it consistent and actually how to query it.
How do I connect the the variables which are contained within elements and the elements that are contained within the data sheets. How do I check when one element or variable is being modified, which data sheets need to be recompiled since they are using the same variables and/or elements?
The more I think about this, the more it sounds like I need to write my own search tree based on an object oriented inheritance class structure and must not use data bases. Can somebody convince me that a data base is the right tool for my issue?
I learned data bases once but this is quite some time ago and to be honest the university was not giving good lectures since we never created a database by our own but only worked on existing ones.
To be more specific, my knowledge leads to this solution so far without knowing how to correctly query for a list of data sheets when changing the content of one value since the reference is a text containing the name of a table:
screen shot since I'm a greenhorn
Update:
I think I have to search for unique connections, so it would end up in many-to-many tables. Not perfectly happy with it but I think I can go on with it.
still a green horn, how are you guys using correct high lightning for sql?
I was making my high school project and decided to use something like nested linked lists for some bonus marks. The aim of my project was to create a digital diary containing infinite no of pages and infinite no of lines per page. My program uses a linked list as a queue and each element in the queue has its own linked list as a queue. I am using arrays for headings and for each sub unit (line) of the nested queue and the gets and puts for input/output. My program displays the input data but not all correctly, the last elements of the array are sometimes smileys and arrows instead of what I put.I am using a structure for line, a class to use that queue and a derived class for the page which contains the heading, page no and the class containing lines. The derived class objects are now used as the bigger linked list in another class. Also, I wish to save the data to a binary file, please tell me whether should I store it as line by line or page by page. I am using C++
The only thing that comes to my mind is error in pointer dereferencing. Basically, your linked lists are pulling data from the wrong sector in memory. Try going through it again and see whether everything is referenced properly and data input is going where it must. Trying saving the data line by line to avoid again overflows or errors. If successful then try page by page.
I am performing some particle simulations in C++ and I need to keep a list of contacts info between particles. A contact is actually a data struct containing some data related to the contact. Each particle is identified with a unique ID. Once a contact is lost, it is deleted from the list. The bottleneck of the simulation is computing the force (a routine inside the contacts), and I have found an important impact on the overall performance according to the actual way the contact list is organised.
Currently, I am using a c++ unordered_map (hash map), whose key is a single integer obtained from a pair function applied over the two unique IDS of the particles, and the value is the contact itself.
I would like to know if there is a better approach to this problem (organising efficiently the list of contacts while keeping the info of the particles they are related with) since my approach is done just because I read and found than a hash map is fast for both insertion and deletion.
Thanks in advance.
I have a C++ server that manages Users for a game. These Users have unique AccountIDs and almost every look-up for Users on the server involves finding a User from a global map of
std::map<unsigned int, User*>
where unsigned int is the AccountID. This works great except for this new case where I am implementing a friends list. In order to add a friend to someones friend list it needs to be done by Username. I am also running into this problem when inviting people by Username to a chatroom or other "party" type events.
My two current options are:
1) Iterate through the entire Users map, doing a string comparison by Username.
2) Do a database look-up on an indexed Username column and return the AccountID, then do a map find for the User*.
Both of these solutions are very inefficient. I am looking for a more optimized solution of finding a User by Username.
The first idea that comes to mind is a Hashtable that hashes on the Username, but then I have two different data structures (the Hashtable and the Map) that are doing the same thing except one is by AccountID and one is by name.
A second option could be to use the Username as the key for the map, although I can't imagine having a string for a key being too efficient.
Any suggestions on what I should do here? As for some more information on the server, there will be around 1000+ Users and they will be leaving and joining constantly.
C++11 has std::unordered_map which will automagically handle hashing for you, e.g. std::unordered_map<std::string, User*>.
I would suggest just using another map std::map<std::string, User*>. I believe that for an application with ~1000 users it is over-engineering to do hashmaps or more complicated solutions, the string based lookup in map will not be that expensive, practically zero compared to lookup in database.
Maybe, you can use the by-product of having alphabetically sorted users somewhere as well.
I have a database where I store player names that belong to people who have certain items.
The items have and IDs, and subIDs.
The way I am currently storing everything is:
Each ID has its own collection
Within the collection there is a document for each subID.
The document for each subID is layed out like so:
{
"itemID":itemID,
"playerNames":[playerName1, playerName2, playerName3]
}
I need to be able to add to the list of playerNames quickly and efficiently.
Thank you!
If I understood your question correctly, you need to add items to the "playerNames" array. You can use one of the following operators:
If the player names array will have unique elements in it, use $addToSet
Otherwise, use $push