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Arrays basics and questions
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‎#2 - Arrays/#0 - array-basics.js‎

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// Arrays in Javascript
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// Decalaration
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let person = {
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name: "Piyush",
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age: 25,
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};
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let arr = ["apple", "banana", "cherry", person];
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console.log(arr.length); // know the length of an array
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// # Add and Remove Elements
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// Add to End of the Array
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arr.push("orange");
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// Remove From End of the Array
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arr.pop();
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arr.pop();
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// Add to Top of the Array
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arr.unshift("orange");
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// Remove From Top of the Array
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arr.shift();
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// # Looping Arrays
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// For Loop
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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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// While Loop
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let i = 0;
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while (i < arr.length) {
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// console.log(arr[i]);
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i++;
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}
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// # Inbuilt Loop Methods
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const numbers = [1, 2, 3, 4, 5];
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// map in javascript
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numbers.map((item, index, array) => {
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return item + 5;
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});
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// filter in javascript
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numbers.filter((item, index, array) => {
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return item > 3;
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});
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// reduce in javascript
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numbers.reduce((prev, item) => {
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return prev + item;
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}, 2);
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// some in javascript
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numbers.some((item, index, array) => {
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return item > 3;
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});
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// every in javascript
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numbers.every((item, index, array) => {
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return item < 10;
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});
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// find in javascript
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numbers.find((item, index, array) => {
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return item > 3;
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});
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// findIndex
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const index = [1, 2, 3].findIndex((item) => item === 2);
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// console.log(index);
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// Spread and Rest Operators
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const nums = [1, 2, 3];
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const nums2 = [4, 5, 6, 7];
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const finalNums = [...nums, ...nums2]; // Spread Operator
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// Rest Operator
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function sum(...numbers) {
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return numbers;
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}
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console.log(sum(nums, nums2, 5, "hello"));
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// # More Array Methods
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// concat
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nums.concat(nums2, arr);
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// Slice
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arr.slice(-2);
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// Splice
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arr.splice(1, 2, "orange");
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// Fill
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const dummy = [2, 5, 1, 6];
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dummy.fill(2, 2);
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// Flat
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const flatEx = [1, [2, 3], [[4, 5], 6]]; // => [1,2,3,4,5,6]
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const flattenedArray = flatEx.flat(2);
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// console.log(flattenedArray);
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// reverse
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nums.reverse();
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// console.log(nums);
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// sort
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const unsorted = [5, 2, 10, 7, 3, 1];
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unsorted.sort((a, b) => b - a);
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console.log(unsorted);
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// Ques 1 - Second Largest Number
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// Given an array Arr of size N, print second largest
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// distinct element from an array.
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// Input: [12, 35, 1, 10, 34, 1] ----->>>>> Output: 34
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// Input: [10, 5, 10] ----->>>>> Output: 5
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// Brute Force Approach
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function secondLargest(arr) {
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const uniqueArr = Array.from(new Set(arr)); // O(n)
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uniqueArr.sort((a, b) => {
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// O(nlogn)
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return b - a;
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});
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if (uniqueArr.length >= 2) {
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return uniqueArr[1];
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} else {
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return -1;
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}
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}
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// console.log(secondLargest([10, 5, 10]));
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// Time Complexity -> O(nlogn);
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// Optimised Approach
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// [12, 35, 1, 10, 34, 1]
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// secondLargest = 34
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// largest = 35
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function secondLargestOptimised(arr) {
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let largest = Number.NEGATIVE_INFINITY;
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let secondLargest = Number.NEGATIVE_INFINITY;
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for (let i = 0; i < arr.length; i++) {
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if (arr[i] > largest) {
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secondLargest = largest;
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largest = arr[i];
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} else if (arr[i] != largest && arr[i] > secondLargest) {
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secondLargest = arr[i];
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}
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}
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return secondLargest;
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}
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console.log(secondLargestOptimised([10, 5, 10]));
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// Time Complexity -> O(n);
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// Space Complexity -> O(1);
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// Ques 2 - Rotate Array by K
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// Given an integer array nums, rotate the array to the right by k steps,
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// where k is non - negative.
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// Input: nums = [1,2,3,4,5,6,7], k = 3 ----->>>>> Output: [5,6,7,1,2,3,4]
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// Input: nums = [-1,-100,3,99], k = 2 ----->>>>> Output: [3,99,-1,-100]
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// Brute Force Approach
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function rotateArray(nums, k) {
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let size = nums.length;
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if (size > k) {
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k = k % size;
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}
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const rotated = nums.splice(size - k, size); // [5, 6, 7]
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nums.unshift(...rotated);
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return nums;
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}
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// Time Complexity - O(n)
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// console.log(rotateArray([1, 2, 3, 4, 5, 6, 7], 3));
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// Optimised Approach
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function rotateArrayOptimised(nums, k) {
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let size = nums.length;
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if (size > k) {
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k = k % size;
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}
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reverse(nums, 0, nums.length - 1); // O(n)
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reverse(nums, 0, k - 1); // O(k)
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reverse(nums, k, nums.length - 1); // O(n-k)
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return nums;
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}
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// Time Complexity -> O(n)
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// Space Complexity -> O(1)
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function reverse(nums, left, right) {
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while (left < right) {
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const temp = nums[left];
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nums[left++] = nums[right];
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nums[right--] = temp;
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}
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}
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console.log(rotateArrayOptimised([-1, -100, 3, 99], 2));
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// Ques 3 - Remove Duplicates from Sorted Array
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// Given an integer array nums sorted in non-decreasing order, remove
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// the duplicates in-place such that each unique element appears
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// only once.The relative order of the elements should be kept
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// the same.Then return the number of unique elements in nums.
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// Input: [1,1,2] ----->>>>> Output: 2, [1,2,_]
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// Input: [0,0,1,1,1,2,2,3,3,4] ----->>>>> Output: 5, [0,1,2,3,4,_,_,_,_,_]
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// With JS Methods
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function removeDuplicates(nums) {
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for (let i = 0; i < nums.length - 1; i++) {
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// O(n)
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if (nums[i] === nums[i + 1]) {
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nums.splice(i + 1, 1); // O(1)
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i--;
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}
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}
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return nums.length;
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}
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// Time Complexity - O(n)
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// Space Complexity - O(1)
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// console.log(removeDuplicates([1, 1, 2]));
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// Without JS Methods - Two pointer Approach
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function removeDuplicatesNew(nums) {
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if (nums.length === 0) return 0;
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let i = 0;
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for (let j = 1; j < nums.length; j++) {
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if (nums[i] !== nums[j]) {
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i++;
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nums[i] = nums[j];
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}
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}
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return i + 1;
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}
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// Time Complexity - O(n)
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// Space Complexity - O(1)
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console.log(removeDuplicatesNew([0, 0, 1, 1, 1, 2, 2, 3, 3, 4]));

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