CS252 Algorithms
Monday, 25 March 2024

https://cs.carleton.edu/faculty/jondich/courses/cs252_s24/

+ Hi!
- Jeff, Olin 301A, jondich
- Office Hours: 301A + Zoom
    see my Carleton-only Google doc w/ Zoom link
    that I mostly remember to turn on

+ Moodle & the course website: what's the deal?

+ Prefect: Kiri Salij

+ Where we're heading
- Articulating computational problems
    clearly, precisely, formally
- Devising algorithms to solve those problems
    and articulating the solutions
    clearly, precisely, formally
- Analyzing algorithms
    runtime, memory use, correctness
- Important classes of algorithms
    greedy, divide-and-conquer, dynamic programming...
- (Not intractability--that's in CS254 Comp & Comp)

+ This is in part a writing class, with a specialized audience

+ What algorithms do you know by name?
    Linear search   O(N)
    Binary search   O(log N)
    Merge sort      O(N log N)
    Quicksort       O(N^2) -- typically this is the library sort()
    Insertion sort  O(N^2)
    Selection sort  O(N^2)
    Bubble sort     O(N^2)
    Radix sort      O(N)
    Bogo sort       O(N!)

    Brute force [super generic]
    Dijkstra's Algorithm
    Regular expression matching
    Back propagation
    Floyd's Algorithm
    ...
 
    Paradigms: greedy, 

  What data structures do you know by name?
    Heap
    Array
    Linked list
    Hash table 
    Binary search tree
    Priority queue
    Stack
    Red-black tree
    Queue
    Graph

    Abstract data types: what is it? (data)
                         what operations can you perform on it? (methods)

+ Articulating a computational problem
- Pick a problem that is solved algorithmically in
    software/hardware that you use
- What are the inputs?
- What are the outputs, and what relationship
    do they bear to the inputs?

- Internet search
    in:
        word(s) (the search term)
        all the web pages & other stuff available on the web
        everybody else's past searches & what they clicked on
        searcher's location
        searcher's chosen natural language
        searcher's past searches
        ...
    out:
        a bunch of URLs, sorted by "relevance"

- The word game "ghost"
    (what problem are we solving?)(AI's optimal strategy)
    in:
        queue of letters stated so far
        the alphabet
        dictionary
    out: 
        a letter (representing the AI's next move)
            (could output an error condition saying "not possible")
            (desire: if a non-word is possible, then the
                output makes one of those; if it's possible
                to force the opponent to lose, do that...)

- YouTube recommendation
    in: 
    out: 

- Google maps (route-finding)
    in: 
    out: 

+ General logistics
- Website & Slack #announcements
- Reading reactions
    - #readings channel
    - include specified hashtag
    - 1 point apiece; drop the lowest two scores
- Problem sets
    - out on Friday (except #1, which is out on Monday)
    - checkpoint submission due 5PM Tuesday
    - final submission due 5PM Friday

+ This week
- Getting our homework and communication system up and running
- First problem set: review stuff from CS201, CS202/Math236
- Remembering how to use LaTeX
- Review of computational complexity
    - O, Ω, ϴ
    - worst-case analysis
    - common complexity classes (e.g., O(n log n))

+ Upcoming due dates
- 5PM Tuesday 3/26: checkpoint for problem set #1
- 11:59PM Wednesday 3/27: reading reaction #1
- 5PM Friday 3/29: problem set #1
- 11:59PM Sunday 3/31: reading reaction #2