Prottoy2938

function makeId(length) {
  let result = "";
  const characters =
    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
  const charactersLength = characters.length;
  for (let i = 0; i < length; i++) {
    result += characters.charAt(Math.floor(Math.random() * charactersLength));
  }
  return result;
}

Prottoy2938

//get the nth number in fibonacci sequence, base case is 0 and 1.

//solution 1, easier to understand but it's not good. It has a time complexity of O(2^n).
function fib(num) {
  if (num === 2) return 1;
  if (num === 1) return 0;
  return fib(num - 1) + fib(num - 2);
}
fib(6) //returns 5

Prottoy2938

{
  "Status": "Connected",
  "Adminstration Control": {
    "Connection": "stable",
    //Total number 100. 70 means adminstration can control most of stuff of that device, but he is restricted on some of the part.
    //will need to think more about it
    "Permission": "70" //rank system. 70 out of 100
  },

  "Device": {

Prottoy2938

//get the nth number in fibonacci sequence, base case is 0 and 1.

//solution 1, easier to understand but it's not good. It has a time complexity of O(2^n).
function fib(num) {
  if (num === 2) return 1;
  if (num === 1) return 0;
  return fib(num - 1) + fib(num - 2);
}
fib(6) //returns 5

Prottoy2938

// Get Fibonacci Sequence in an Array, base case is 0 and 1.

const fibSequence = (num) => {
    if(num === 0) return 0;
    const arr=[0,1];
    let counter=2;      
    while(counter <=num){
        arr[counter]=arr[counter -1] + arr[counter -2]
        counter ++
    }

Prottoy2938

//Solution 1

const isValidBST = function(root, min = Number.MIN_SAFE_INTEGER, max = Number.MAX_SAFE_INTEGER) {
    if(root == null) return true
    if(root.val >= max || root.val <= min) return false
    return isValidBST(root.left, min, root.val) && isValidBST(root.right, root.val, max)
};

Prottoy2938

//Dijkstra algorithm is used to find the shortest distance between two nodes inside a valid weighted graph. Often used in Google Maps, Network Router etc.

//helper class for PriorityQueue
class Node {
  constructor(val, priority) {
    this.val = val;
    this.priority = priority;
  }
}

Prottoy2938

//Helper class. To get the most prioritize result out
class PriorityQueue {
  constructor() {
    this.values = [];
  }
  enqueue(val, priority) {
    this.values.push({ val, priority });
    this.sort();
  }
  dequeue() {

Prottoy2938

In graph theory, a tree is an undirected graph in which any two vertices are connected by exactly one path,
or equivalently a connected acyclic undirected graph.

Which means, in a graph, we can reach a certain node in many different ways, but in a tree there should be only ONE way to reach that node.

Prottoy2938

//The algorithm starts at the root node and explores as far as possible along each branch before backtracking
//To simplify, In Depth First Search in Binary Search Tree, travels through one side until it reaches its end and then tries the other side.

//============================================================================================================
//DFS_PreOrder
//This method, visits the one specific side(either left or right) at once, and after the whole side is finished, then visits the other side.
// as it goes through the tree, it pushes visited node continuously.
//Example:   10
//      6          15
//   3    8            20