r/computerscience

So the proof to my understanding goes like this:

Imagine a machine A which takes in a machine B's code and that B's input as its own input and tells us if the problem halts exists

Place A into a greater machine C which takes the output of A and if A returns "halts" it goes into an infinite loop, and if it returns "does not halt" C halts.

Use C as an input to C and create a paradox.

The part I don't understand is how exactly the last step is a paradox. A, and therefore C don't just take in a machine as an input, but also that machines input, so you can't just put the machine C into itself without the context of what is being put into C.

Therefore C(C(B)) is not the same program as C(B), so why do they need to have the same result in order for it not to be a paradox?

Edit: i think i get it now, C modifies A not just in how it reacts to the output but it also modifies the input to be the same for both the program and the program's input

Thanks to u/OpiskionThemed, u/Aminumbra and u/stevemegson for explaining it

By simple I mean small. Maybe a simple for loop or a state machine with less than 10 states. For example game of life has a pretty simple algorithm and It can probably be made in this manner. What about embedded systems though? Most embedded projects I see use the CPU as a data retriever and sender.

I'm doing a research and I would really appreciate some sources. Articles, videos, books whatever.

It would have functionally no use and would never be spoken. I still say we need a name for it.

I'm doing some research to better understand the software engineers actually use in industry and where the biggest productivity pain points are.

I'm interested in both professional tools and the smaller utilities you can't live without.

Some examples:
\\\\- CAD: SolidWorks, CATIA, Creo, Inventor, Fusion 360, NX
\\\\- Simulation: ANSYS, Abaqus, COMSOL
\\\\- Electrical: Altium Designer, KiCad, OrCAD, LTspice, PSpice
\\\\- Controls: MATLAB/Simulink, LabVIEW
\\\\- PLC/SCADA: TIA Portal, Studio 5000, Ignition
\\\\- Programming: VS Code, Visual Studio, Eclipse
\\\\- Other engineering tools you use regularly

A few questions:

\\\\- Which software do you spend the most time in?
\\\\- What's the most repetitive or frustrating task you do every day?
\\\\- Is there a feature you've always wished existed but still doesn't?
\\\\- Are there tasks you still have to do manually because the software makes them painful?
\\\\- If you could improve one engineering tool tomorrow, what would you add?

I'm especially interested in hearing from mechanical, electrical, civil, controls, embedded, HVAC, manufacturing, and automation engineers, but I'd love to hear from anyone.

Not trying to sell anything—I'm just trying to understand where engineers lose the most time so I can identify opportunities for better tools. Looking forward to hearing what drives you crazy every day.

Would it be possible to build a PC motherboard that utilizes both DDR5 and DDR4 RAM simultaneously? Ideally, it would use DDR5 for speed intensive processes, then DDR4 for background tasks or virtual machines, and be able to swap fairly quickly between the memory banks (faster than loading from disk). This seems very efficient, cost effective, and even reduces e-waste. Given the state of memory market, it would allow people to tap into lower-cost markets and utilize parts that would end up at best in a recycling plant and at worst in a landfill.

I understand that having a motherboard would only be the literal first step: then you would need a whole host of operating system support, but would you ALSO require the CPU itself to support such a feature?

Just something manufacturers should be considering given the market outlook.

I want to learn string algos like KMP, Z-func and rolling hash. Pls suggest some good yt channels and articles for that. Also should i learn them or are they too advanced (I am between beginner and intermediate in dsa).

Title. Ive been studying systems programming (csapp, ostep, database fundamentals) for a few weeks now and thought id like to explore cyber security since it ties closely to what im learning (heard it on reddit).

What type of different topics are there in cyber security and what books or resources can I study to explore them? Also are certifications necessary in this field as someone who cant afford one?

google jewels-and-stones on the leet site. sorry cant give a link as reddit for reason wont allow me to post this as "I'm beaking rule 1"

Tldr: given 2 character lists, find all character in List 2 that are in List 1

All the "solutions" for this question seem to be only using sets but,

We can observe that the list is only limited to ASCII character, thus only having 256 possible character

Thus we initialize a fixed size array of 256 elements and just set the elements whose index matches to the filter characters to true

then we walk the list we and to check and just ask , "is the character true in our array?"

example implmentation

#include <string>
#include <array>
int numJewelsInStones(std::string jewels, std::string stones) {
      std::array<char, 256> jewels_set = {};
          for (const char &i : jewels) {
              jewels_set[(unsigned char)i] = true;
      }
    int count = 0;
    for (const char &i : stones) {
      if (jewels_set[(unsigned char)i]) {
        count++;
      }
    }
    return count;
  }

i dont get it. unordered set/hasmap has the overhead of hashing the elements, and the hash is usually less space efficient that just creating a 256 array holding all possible representations of the filter

I'm considering studying Christopher Bishop's Pattern Recognition and Machine Learning to strengthen my understanding of the theoretical foundations of machine learning.

Although the book is almost 20 years old, it is still frequently recommended. For someone primarily interested in the underlying theory rather than the latest deep learning techniques, how well has it held up? Are there any modern texts that cover the same fundamentals more effectively?