Is it possible to model arrays as functions while preserving O(1) access times?

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• React-dnd multiple elements

  I can make react-dnd drag easily having a single element to drag over however I have array of 4 fields I'd like to make draggable. In my example code down below it creates four boxes from mapping the array and each box has a className of 'element'. Which should make them all draggable however they won't move.

  Here is my drag code:

   const ELEMENT = 'element';
      const [{ isDragging }, drag, dragPreview] = useDrag(() => ({
        type: ELEMENT,
        collect: (monitor) => ({
          isDragging: monitor.isDragging()
        })
      }))
  

  Here is my draggable element:

   {FieldDetail.map((e,i) =>  
     <div key={i} ref={dragPreview} style={{ opacity: isDragging ? 0.5 : 1}}>
          <div className='element' ref={drag}></div>            
      </div>          
    )} 
  

  Any ideas? Do I need to do something more within the type or className?
• how to send long complex array with socket.io?

  I have complex an array containing lots of base64 data. and I send this array to server with socket.io. If I send an array containing one or two base64 data. the function is working successfully. but if I send an array containing lots of base64 data. function does not react.

  my purpose

  • client will prepare templates.
  • When the client clicks the save button, it sends this template to the server with socket.io.
  • templates sent to the server will be saved to hdd with nodejs.

  my array template

  const MyArray = [
  {
  div_id:div.id,
  div_innerhtml:div.innerHTML,  //<img src=base64...
  div_backgroundimage : div.backgroundimage //base64... 
  }
  ]
  

  client-side code

  const MyArray=[],SaveBtn = document.queryselector("#save_div");
      
  const SendArray = (ARRAY)=>{
      socket.emit("div_data",ARRAY);
  }
  
  SaveBtn.onclick = ()=>{
      SendArray(MyArray);
  }
  

  server-side code

  socket.on("div_data",(data)=>{
      console.log(data)   // function does not react.
      let JSON_DATA = JSON.stringify(data)
      console.log(JSON_DATA)   // function does not react.
  });
  

  Is this socket.io error? What should I do or how should I research this issue?

  UPDATE

  network tab in devtools

  for two base64 image : (function work successfully)

  

  for four base64 image : (function does not react)

  
• Program to find smallest 5 values in a matrix using C

  I'm trying to find the smallest 5 values in a 6*6 matrix using C. Note I was successful in finding the least value as well as finding the least values from a 1D array, but could not make it to iterate and get the least 5 values of the matrix using 2D. Any ideas appreciated.

  [The sample of a matrix I want to sort and get the lowest values]

  2.36^2	5.01^2	1.00^3
  1.25^3	1.09^2	2.98^2
  1.09^2	2.50^3	1.81^5
• Is there a way to use streams to return value from doing operations on elements

  I have a Train class, with a List<TrainCar> containing objects from a TrainCar class. I have a function in Train called getTotalWeight(). Each TrainCar has a function called getWeight() which returns a value. Can I use streams in some way to make the body of the getTotalWeight() function looking like this?

  return cars.stream().//some function//;
  
• Lodash/fp pipe functionality

  I am learning functional programming in JavaScript. I am using the pipe function from lodash. The code run successfully but It shows some problems I can not figure out.

  The Code

  const { pipe } = _;
  
  const trimText = (input) => input.trim();
  const wrap = (type) => (
      (input) => (
          `<${type}>${input}</${type}>`
      )
  );
  const transform = pipe(trimText, wrap('span'));
  console.log(transform('Javascript'));

  <script src='https://cdn.jsdelivr.net/g/lodash@4(lodash.min.js+lodash.fp.min.js)'></script>

  The problems

  Argument type function(any): any is not assignable to parameter type () => any.
  Invalid number of arguments, expected 0
  
• Lexical analyzer in Scala and Functional Programming

  I am taking a compiler design class and this assignment is part of a bigger project to build a simple compiler. Our teacher told us to use the language of our choice to implement a lexical analyzer that recognizes comments in C-like languages, floating-point literals, if-statements, for-loops, while-loops, and do-while loops.

  The book gives an example of a lexical analyzer written in C that recognizes integer literals and identifiers. The example uses macros to define token codes and character classes. It uses impure functions and global mutable variables. Coming to think of implementing a lexical analyzer myself after designing the finite state machine, I am having a hard time avoiding mutability.

  I want a function with this signature:

  def lex(sourceUnit: Array[Char]) : Int = {
  
  }
  

  This function is supposed to take a an array of characters, find out whether it's a comment or a floating-point literal and return the token code. I can't use a for loop. I can't initialize a variable called "lexeme" and gradually add characters to it. I am not sure how to start. How should I achieve what I have in mind in a pure way?
• How to find nearest value in binary search?

  I have implemented a binary search in C#, and figured out a way to find duplicate values, however now i wanted to see if there is a way to find the nearest value and position of the key being searched for if that key doesn't exist in the array.Could someone guide me on how i would do this?
• Time complexity of a nested loop which goes from 0 to a max/min value

  I'm having a hard time trying to find something similar to my situation.

  The pseudo-code:

  int n = some pre-defined value
  int d = some pre-defined value (that is at max the same as n, don't know if that's relevant)
  
  for (i = 0; i < n; i++) {
      for (int j = 0; j < Min(i, d); j++) {
          do something
      }
  }
  
  

  I get that the first loop runs n times which means the time complexity itselft is O(n), but I cannot understand what is the time complexity of the second loop.

  Thanks in advance.
• What is the time complexity of my solution that is using TreeSet?

  I've implemented a solution to a problem using TreeSet in Java. For every provided element from an array of size m, I add the element to the set and then read its previous and next values.

  So for every element from the unsorted array of size m:

  • I add the element to the tree: t_set.add(number)
  • then I read the next and previous values of the added element from the tree:

  prev = t_set.lower(number);
  next = t_set.higher(number);
  

  Where t_set is the tree set.

  Since all 3 of those operations are log(n) - where n is the number of nodes in the tree - I think my time complexity for every input is 3*log(n).

  Now if I'm correct the time complexity for the entire solution is 3* m*log(n)? I'm not sure about that since m could be a huge number but n starts at 0 and increments as more items are added.

  Also if there is a more efficient structure than treeset (numbers have to sorted), please let me know.