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‎Array/README.md

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# Array Manipulation in JavaScript: From Basics to Advanced
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### How do you create an empty array in JavaScript?
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```javascript
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const arr = [1, 2, 3, 4, "Hello", {name: "Vishal"}, [1,2,3], 4];
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// const arr2 = new Array();
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console.log(arr);
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```
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### How do you access the first and last elements of an array?
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```javascript
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const firstElement = arr[0]; // O(1)
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const arrLength = arr.length;
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const lastElement = arr[arrLength - 1];
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console.log(firstElement, arrLength, lastElement);
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```
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### How do you remove the last element from an array?
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```javascript
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const lastElement1 = arr.pop(); // O(1)
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console.log(arr, lastElement1);
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```
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### How do you add an element to the end of an array?
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```javascript
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arr.push(5); // O(1)
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console.log(arr);
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```
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### How do you add an element to the start of an array?
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```javascript
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arr.unshift(0); // O(N)
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console.log(arr);
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```
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### How do you remove the first element from an array?
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```javascript
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arr.shift(); // O(N)
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console.log(arr);
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```
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### How do you loop through an array in JavaScript?
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```javascript
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for (let i = 0; i < arr.length; i++){
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console.log(arr[i]);
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}
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arr.forEach((x, i) => {
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console.log(x);
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});
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for (let x of arr){
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console.log(x);
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}
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```
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### Question 1: How do you check if an element exists in an array?
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```javascript
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const findElement = (arr, target) => {
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for (let x of arr){
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if (x === target){
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return true;
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}
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}
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return false;
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}
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console.log(findElement(arr, "Hello"));
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console.log(findElement(arr, "H"));
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console.log(arr.includes("Hello"));
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```
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### Question 2: How do you find the index of an element in an array?
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```javascript
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const findElementIndex = (arr, target) => {
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for (let i = 0; i < arr.length; i++){
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if (arr[i] === target){
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return i;
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}
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}
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return -1;
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}
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console.log(findElementIndex(arr, "Hello"));
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console.log(arr.indexOf("Hello"));
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```
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### How to delete, add & update elements from a specific index?
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```javascript
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console.log(arr);
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arr.splice(1, 3);
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console.log(arr);
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arr.splice(1, 0, 2, 3, 4, 5, 6);
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console.log(arr);
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arr.splice(1, 3, 6, 7, 8);
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console.log(arr);
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```
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### `splice()` vs `slice()`
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```javascript
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const subArr = arr.slice(1, 4); // [start, end)
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console.log(subArr);
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```
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### Shallow Copy of Array
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```javascript
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const arrB = arr;
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arrB.splice(1, 4);
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console.log(arrB, arr);
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```
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### Deep Copy of Array
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```javascript
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const arrC = [...arr];
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const arrD = Array.from(arr);
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const arrE = arr.concat();
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arrC.splice(1, 4);
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arrD.splice(1, 4);
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arrE.splice(1, 3);
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console.log(arrC, arrD, arrE, arr);
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```
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### How to concatenate two arrays in JavaScript?
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```javascript
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const newArr = [...arr, ...arrE];
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const newArr2 = arr.concat(arrE);
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console.log(newArr, newArr2);
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```
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### Question 3: How can you check if two arrays are equal?
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```javascript
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const isArrayEqual = (arr1, arr2) => {
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if (arr1.length !== arr2.length){
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return false;
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}
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for (let i = 0; i < arr1.length; i++){
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if (arr1[i] !== arr2[i]){
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return false;
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}
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}
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return true;
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// One Line solution
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// return arr1.length === arr2.length && arr1.every((ele, i) => arr1[i] === arr2[i]);
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}
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console.log(isArrayEqual([1, 2, 3], [1, 2, 3]));
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```
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### Question 4: How to sort an array in ascending and descending order?
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```javascript
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const x = [1, 4, 6, 0, -9, -5];
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x.sort(); // O(NlogN)
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console.log(x);
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x.sort((a, b) => b - a);
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console.log(x);
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```
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### Question 5: How to reverse an array?
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```javascript
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x.reverse();
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console.log(x);
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```
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### Map, Filter & Reduce
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```javascript
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const newMapArr = x.map((ele, i) => ele * ele);
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console.log(newMapArr);
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const positiveNumbers = x.filter((ele, i) => ele > 0);
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console.log(positiveNumbers);
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const sumOFArr = positiveNumbers.reduce((acc, ele) => acc + ele);
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console.log(sumOFArr);
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```
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### Flat: [1, 2, 4, 5, 6, 7, 8, 9]
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```javascript
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const y = [1, 2, [4, 5, [6, 7]], 8, 9];
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const flattedArray = y.flat(2);
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console.log(flattedArray);
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```
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### `filter()` vs `find()`
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```javascript
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const positiveNumber = x.find((ele, i) => ele > 0);
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console.log(positiveNumber);
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```
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# Practice Questions
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- [Two Sum](https://leetcode.com/problems/two-sum/)
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- [Majority Element](https://leetcode.com/problems/majority-element/)
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- [Remove Duplicates from sorted array](https://leetcode.com/problems/remove-duplicates-from-sorted-array)
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- [Squares of a Sorted Array](https://leetcode.com/problems/squares-of-a-sorted-array)
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- [Find Pivot Index](https://leetcode.com/problems/find-pivot-index/)
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- [Move Zeroes](https://leetcode.com/problems/move-zeroes)
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- [Remove Element](https://leetcode.com/problems/remove-element)
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- [Max Consecutive Ones](https://leetcode.com/problems/max-consecutive-ones/)

‎Basics/README.md

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# Practise Loop, functions & Math Problems
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### Question 1: sum of all natural numbers from 1 to n
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### Question 1: Sum of all natural numbers from 1 to n
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```javascript
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function sumOfNaturalNumber(num){
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return sum;
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}
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console.log(sumOfNaturalNumber(5)) //15
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console.log(sumOfNaturalNumber(10)) //55
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console.log(sumOfNaturalNumber(8)) //36
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console.log(sumOfNaturalNumber(5)); // 15
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console.log(sumOfNaturalNumber(10)); // 55
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console.log(sumOfNaturalNumber(8)); // 36
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```
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### Question 2: Sum of digits of a number
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```javascript
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return sum;
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}
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console.log(sumOfDigits(1287)) //18
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console.log(sumOfDigits(1287)); // 18
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```
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### Question 3: count the number of digits of a number
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### Question 3: Count the number of digits of a number
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```javascript
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function countDigits(num){
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return count;
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}
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console.log(countDigits(121)) //3
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console.log(countDigits(-1211413131)) //10
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console.log(countDigits(121)); // 3
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console.log(countDigits(-1211413131)); // 10
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```
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### Question 4: Given an integer x, return true if x is a palindrome, and false otherwise.
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A palindrome number is a number that remains the same when digits are reversed
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### Question 4: Check if a number is palindrome
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```javascript
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let isPalindrome = function(x) {
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let copyNum = x, reverseNum = 0;
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while(copyNum > 0){
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const lastDigit = copyNum%10;
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reverseNum = reverseNum*10 + lastDigit;
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copyNum = Math.floor(copyNum/10)
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const lastDigit = copyNum % 10;
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reverseNum = reverseNum * 10 + lastDigit;
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copyNum = Math.floor(copyNum / 10);
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}
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return x === reverseNum
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return x === reverseNum;
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};
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console.log(isPalindrome(121)) //true
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console.log(isPalindrome(1234)) //false
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console.log(isPalindrome(121)); // true
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console.log(isPalindrome(1234)); // false
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```
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### Question 5: Find nth fibonacci number
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### Question 5: Find nth Fibonacci number
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The Fibonacci numbers, commonly denoted F(n) form a sequence, called the Fibonacci sequence,
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such that each number is the sum of the two preceding ones, starting from 0 and 1.
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}
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return next;
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};
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// Fibonacci Sequence: 0 1 1 2 3 5 8...
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console.log(fib(5)) // 5
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console.log(fib(10)) //55
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console.log(fib(5)); // 5
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console.log(fib(10)); // 55
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```
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### Question 6: Missing Number
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### Question 6: Missing Number in an Array
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Given an array nums containing n distinct numbers in the range [0, n],
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return the only number in the range that is missing from the array.
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```javascript
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let missingNumber = function(nums) {
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let sum = 0;
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return nums.length*(nums.length+1)/2 - sum;
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};
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// One Line Solution:
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let missingNumber = (nums) => nums.length*(nums.length+1)/2 - nums.reduce((acc, num) => num + acc);
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console.log(missingNumber([3,0,1])) //2
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console.log(missingNumber([9,6,4,2,3,5,7,0,1])) //8
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console.log(missingNumber([3,0,1])); // 2
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console.log(missingNumber([9,6,4,2,3,5,7,0,1])); // 8
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```
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# Practice Questions
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- [Count odd Numbers in an Interval Range](https://leetcode.com/problems/count-odd-numbers-in-an-interval-range/)
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- [Count Odd Numbers in an Interval Range](https://leetcode.com/problems/count-odd-numbers-in-an-interval-range/)
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- [Fizz Buzz](https://leetcode.com/problems/fizz-buzz/)
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- [Power of Two](https://leetcode.com/problems/power-of-two/)
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- [Find Square root of a Number](https://leetcode.com/problems/sqrtx/)
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- [Find Square root of a Number](https://leetcode.com/problems/sqrtx/)

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