What is Array? (original) (raw)

Last Updated : 12 Apr, 2025

Array is a linear data structure where all elements are arranged sequentially. It is a collection of elements of **same data type stored at **contiguous memory locations.

For simplicity, we can think of an array as a flight of stairs where on each step is placed a value (let's say one of your friends). Here, you can identify the location of any of your friends by simply knowing the count of the step they are on.

This makes it easier to calculate the position of each element by simply adding an **offset to a base value, i.e., the memory location of the first element of the array (generally denoted by the name of the array). The base value is index 0 and the difference between the two indexes is the **offset.

**Is the array always of a fixed size?

Arrays at core are of fixed size only, but most of the languages provide dynamic sized arrays using the underlying fixed sized arrays. For example, vector in C++, ArrayList in Java and list in Python. In C language, the array has a fixed size meaning once the size is given to it, it cannot be changed i.e. you can’t shrink it nor can you expand it.

**Important Points to Note about Arrays

• Array is a fundamental data structure and used to implement other data structures like stack, queue, dequeue and heap.
• The main advantages of using array over other data structures are cache friendliness and random access memory. Please refer **Getting Started with Array Data Structure for more details.

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Basic operations in Array

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Easy problems on Array

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• Second Largest Element in an Array Given an array of positive integers arr[] of size n, the task is to find second largest distinct element in the array.Note: If the second largest element does not exist, return -1. Examples:Input: arr[] = [12, 35, 1, 10, 34, 1]Output: 34Explanation: The largest element of the array is 35 and the sec 14 min read

• Move all zeros to end of array Given an array of integers arr[], the task is to move all the zeros to the end of the array while maintaining the relative order of all non-zero elements.Examples: Input: arr[] = [1, 2, 0, 4, 3, 0, 5, 0]Output: arr[] = [1, 2, 4, 3, 5, 0, 0, 0]Explanation: There are three 0s that are moved to the end 15 min read

• Rearrange array such that even positioned are greater than odd Given an array arr[], sort the array according to the following relations: arr[i] >= arr[i - 1], if i is even, ∀ 1 <= i < narr[i] <= arr[i - 1], if i is odd, ∀ 1 <= i < nFind the resultant array.[consider 1-based indexing]Examples: Input: arr[] = [1, 2, 2, 1]Output: [1 2 1 2] Expla 9 min read

• Rearrange an array in maximum minimum form using Two Pointer Technique Given a sorted array of positive integers, rearrange the array alternately i.e first element should be a maximum value, at second position minimum value, at third position second max, at fourth position second min, and so on. Examples: Input: arr[] = {1, 2, 3, 4, 5, 6, 7} Output: arr[] = {7, 1, 6, 2 6 min read

• Segregate even and odd numbers using Lomuto’s Partition Scheme Given an array arr[] of integers, segregate even and odd numbers in the array such that all the even numbers should be present first, and then the odd numbers.Examples: Input: arr[] = {7, 2, 9, 4, 6, 1, 3, 8, 5}Output: 2 4 6 8 7 9 1 3 5Input: arr[] = {1, 3, 2, 4, 7, 6, 9, 10}Output: 2 4 6 10 7 1 9 3 6 min read

• Reversal algorithm for Array rotation Given an array arr[] of size N, the task is to rotate the array by d position to the left. Examples: Input: arr[] = {1, 2, 3, 4, 5, 6, 7}, d = 2Output: 3, 4, 5, 6, 7, 1, 2Explanation: If the array is rotated by 1 position to the left, it becomes {2, 3, 4, 5, 6, 7, 1}.When it is rotated further by 1 15 min read

• Print left rotation of array in O(n) time and O(1) space Given an array of size n and multiple values around which we need to left rotate the array. How to quickly print multiple left rotations?Examples : Input : arr[] = {1, 3, 5, 7, 9}k1 = 1k2 = 3k3 = 4k4 = 6Output : 3 5 7 9 17 9 1 3 59 1 3 5 73 5 7 9 1Input : arr[] = {1, 3, 5, 7, 9}k1 = 14 Output : 9 1 15+ min read

• Sort an array which contain 1 to n values We are given an array that contains 1 to n elements, our task is to sort this array in an efficient way. We are not allowed to simply copy the numbers from 1 to n.Examples : Input : arr[] = {2, 1, 3};Output : {1, 2, 3}Input : arr[] = {2, 1, 4, 3};Output : {1, 2, 3, 4} Native approach - O(n Log n) Ti 7 min read

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Intermediate problems on Array

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Hard problems on Array

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