Day 1 of #100DaysOfCode

What I learned?

I learned the following topics:

• Two-pointer Approach to solve array problem

• Solved 1 leetcode easy question 283.Move Zeroes

• Solve 1 codeforces question 1360B. Honest Coach

• Object literals, this keyword, instanceof operator, constructor function

What I develop/solved?

• Solved 1 leetcode easy question 283.Move Zeroes

• Solved 1 codeforces question 1360B. Honest Coach which uses greedy and sorting

Code snippet/Screenshots/Notes

1. Leetcode 283. Move all Zeros to the end of the array

• Brute approach

class Solution {
public:
    void moveZeroes(vector<int>& nums) {
        int size = nums.size();

        vector<int> temp; //additonal array

        for(int i = 0; i<size; i++){
            if(nums[i] != 0){
                temp.push_back(nums[i]); //storing non-zeros to additional array
            }
        }  // O(n)

        for(int i = 0; i<temp.size(); i++){
            nums[i] = temp[i]; //put non-zeros to orignal array
        } //O(x)

        for(int i = temp.size(); i<size; i++){
            nums[i] = 0; //fill remaining array with zeros
        }  // O(n-x)
    }
};

Time Complexity: O(n) + O(x) + O(n-x) ~ O(2*n) = O(n) Where n = total no. of elements, x = total no. of non-zero numbers, n-x = total no. of zeros

Space complexity: O(n), because we are using temporary array

• Optimal Approach

class Solution {
public:
    void moveZeroes(vector<int>& nums) {
        int j = -1;

        for(int i = 0; i<nums.size(); i++){
            if(nums[i] == 0){  //finding the first 0 and j is assigned to it
                j = i;
                break;
            }
        }

        if(j == -1){  //it means, there are no zero elements in array
            return;
        }

        for(int i = j+1; i<nums.size(); i++){ //start iterating from j+1
            if(nums[i] != 0){  //finding non-zero element 
                swap(nums[j], nums[i]); //and then swap j'th and i'th element
                j++; //increasing j to make sure it remains on first 0
            }
        }
    }
};

Time complexity: O(n) + O(n) = O(2n) = O(n)

Space Complexity: O(1), because we are not using any extra space to solve the problem

---

2. Codeforces 1360B. Honest Coach(based on greedy and sorting)

#include <bits/stdc++.h>
using namespace std;

void solve()
{
    int n;
    cin >> n;
    vector<int> arr(n, 0);
    for (int i = 0; i < n; i++)
    {
        cin >> arr[i];
    }

    sort(arr.begin(), arr.end());

    int finalAnswer = INT_MAX;

    for(int i = 1; i<n; i++){
        int diff = abs(arr[i] - arr[i-1]);
        if(diff < finalAnswer){
            finalAnswer = diff;
        }
    }

    cout << finalAnswer << endl;
}

int main()
{
    int t;
    cin >> t;
    while (t--)
    {
        solve();
    }
    return 0;
}

---

Objects and classes in JavaScript

• Javascript is a prototype-based language and its classes are primarily syntactic sugar.

• Object is a collection of properties and methods

• Parts of OOPs

  1. Constructor function

  2. Prototypes

  3. Classes

  4. Instances (new, this)

• 4 Pillars of OOPs

  1. Abstraction

  2. Encapsulation

  3. Inheritance

  4. Polymorphism

Object Literal

//object literal

const userDetails = {

    //properties
    username: "randomUsername",
    name: "username",
    loginCnt: 5,
    signedIn: true,

    //methods
    getUserDetails: function () {
        console.log(`username is: ${this.username}`);
    }
}

userDetails.getUserDetails();

This keyword

this keyword refers to the context within which a function is executed

const obj = {
    name: 'John',
    greet: function() {
        console.log('Hello, ' + this.name);
    }
};
obj.greet(); // `this` refers to the `obj` object

instanceof operator

function Animal() {}

const dog = new Animal();

console.log(dog instanceof Animal); // true

Contructor function

   function User(username, loginCount, isLoggedIn) {
   this.username = username
   this.loginCount = loginCount
   this.isLoggedIn = isLoggedIn

   this.greeting = function(){
       console.log(`Hello ${this.username}! How are you?`)
   }

    return this
}

/* Empty object created when use new keyword */

const userOne = new User("ashCode98", 2, true);
const userTwo = new User("random", 1, false);

console.log(userOne)
console.log(userTwo)