Top Conceptual Questions and Answers on Array for Interviews

An Array is a fundamental concept in computer science that stores a collection of elements in a contiguous block of memory. It allows for efficient access to elements using indices and is widely used in programming for organizing and manipulating data.

In our article “Top Array Interview Questions and Answers”, we present a collection of questions focused on Arrays. These problems will help you sharpen your problem-solving skills and prepare effectively for interviews. By tackling these challenges, you can enhance your understanding of Arrays and boost your confidence in interviews. Let’s begin and master Arrays by solving Top Array Problems.

Conceptual Array Interview Questions and Answers

Question 1. What is an Array in Programming?
Answer:

An Array is a linear data structure that stores a collection of elements of same data type in contiguous memory location. For instance, if an array is declared as an “int” type, it can only contain integers, and it cannot accommodate other data types like double, float, or char. The individual elements in an array are accessed via their respective indices.

Question 2. Name some characteristics of Array Data Structure.
Answer:

• Finite (fixed-size): An array is considered finite as it can only hold a specific number of elements.
• Order: The elements in an array are stored sequentially, one after the other, in a linear and orderly manner within the contiguous memory locations of a computer.
• Homogeneous: An array is referred to as homogeneous because all of its elements are of the same data type.

Question 3. Name some Advantages and Disadvantages of Arrays.
Answer:

Advantages:

• Quick Random Access: Fetching an element at a specific index takes O(1) time, irrespective of the array’s size.
• Fast Insertion at the end: Adding a new element to the end of the array is also a quick operation, taking O(1) time.

Disadvantages:

• Fixed Capacity: One of the limitations of an array is that its size is fixed. You need to declare the number of elements it will hold in advance.
• Insertions and Deletions Operations: Inserting or deleting elements can be costly operations because you need to shift other elements to fill or close gaps. These operations take O(n) time in the worst-case scenario.

Question 4. What is time complexity of basic array operations?
Answer:

Arrays store elements in contiguous memory locations, resulting in a space complexity of O(n). This allows for constant time retrieval, O(1), of any element by using its index. Inserting an element at the end of an array is also a constant time operation, O(1). However, if an element is inserted in the middle of an array, all subsequent elements must be shifted, leading to a time complexity of O(n). The O(1) time complexity for appending at the end does not take into account the potential need to resize the array when it’s full, which would require additional time.

Array Operations Time Complexity

• Accessing an element: O(1)
• Inserting/deleting at the end: O(1)
• Inserting/deleting at the beginning/specific index: O(n)
• Searching: O(n)
• Sorting: O(n log n)

Question 5. What is the main difference between an Array and Dictionary?
Answer:

Both arrays and dictionaries are data structures that store collections of items, but they differ in how these items are accessed and organized.

Arrays store objects in an ordered manner and are accessed by index. Dictionaries, however, store key-value pairs and are accessed by key, with no inherent order. Arrays are ideal for sets of objects, while dictionaries are better for showing relationships between pairs of objects.

Question 6. What are Dynamic Arrays?
Answer:

A dynamic array is an enhanced version of an array that overcomes a key limitation: the need for a fixed size. Unlike standard arrays, where you must specify the number of elements it will hold in advance, dynamic arrays can automatically resize themselves as elements are added. This means you don’t need to determine the size of the array ahead of time, making dynamic arrays more flexible and easier to use when the number of elements is not known or can change.

Question 7. What will happen if you do not initialize an Array?
Answer:

Depending on the data type, an array will be initialized with either the default values or garbage values.

Question 8. What is the default value of Array in Java?
Answer:

In Java, if we don’t explicitly assign values, the language automatically initializes them with default values. These are 0 for byte, short, int, and long, 0.0 for float and double, false for boolean, and null for object references.

Question 9. Difference between Array and ArrayList in Java.
Answer:

Question 10. Can you declare an array without assigning the size of an array?
Answer:

No, without specifying a size, we are unable to declare an array. An array declaration without a size will result in a compile-time error.

Question 11. Difference between Array and Object.
Answer:

An object represents an entity with properties, while an array stores a collection of data in a single variable. We access, modify, and delete object properties using brackets and dots, whereas arrays utilize zero-based indexing and built-in methods for manipulation. Iteration over object properties and array items is achieved through various loop mechanisms such as for, for…in, for…of, and forEach().

In Java, all objects are dynamically allocated on the heap, unlike in C++ where objects can be allocated on either the heap or the stack. When using the new() method in C++, objects are allocated on the heap, whereas they are allocated on the stack if not declared as global or static.

Question 12. How to linearly search an element in an array?
Answer:

We will traverse the array and match each element with the element that needs to be searched. Display "Target Found" if the match is found; if not, carry on searching.

Question 13. Why is the complexity of fetching from an Array be O(1)?
Answer:

As Arrays are allocated contiguously in memory, Fetching a value via an index of the array is an arithmetic operation. All arithmetic operations are done in constant time i.e., O(1).

In an array, we have the memory address of index 0 (Base address). By adding the product of the index number (of value to be fetched) and the size of one element (ex. int size is 4 bytes) with the base address, we can have the address of that index’s value. we don’t have to iterate through the array. So it’s done in O(1).

Address of i^th Index = Base address + offset = Address of 0^th Index + i × (size of one element)

Question 14. What is the difference between Array and Linked List?
Answer:

In Array, all elements are stored in contiguous memory locations where as in Linked List, elements are not stored in contiguous memory locations but are connected with the help of pointers where each node stores the address or reference of the next node. Therefore, random access take O(1) time in Array but takes O(N) time in Linked List. Also, Array has a fixed size where Linked List has dynamic size.

Question 15. How can you get the index of an array element?
Answer:

The index of an element can be determined using either a linear or binary search. A linear search involves iterating over each element in an array until the desired element is found. Once the element is located, its index is returned. The time complexity of a linear search is O(n), and it can be applied to both sorted and unsorted arrays.

On the other hand, if the array is sorted, a binary search can be employed. This method repeatedly divides the array in half until the middle element matches the desired element, at which point its index is returned. The time complexity of a binary search is O(log n).

Question 16. How do you merge two sorted arrays into one sorted array?
Answer:

To merge two sorted arrays into one sorted array:

1. Initialize an index for each array, starting from the first element.
2. Compare the elements at the current indices of both arrays.
3. Append the smaller element to the merged array and increment its corresponding index.
4. Repeat steps 2 and 3 until all elements from both arrays are merged into the result array.
5. Return the merged array.

Question 17. What is a Two-Dimensional Array?
Answer:

Two Dimensional Arrays, also known as Matrix are considered as an array of arrays. In each index of two dimensional array, we have another array stored in it. Elements in Two Dimensional Arrays are arranged in rows and columns and require O(1) time for random access.

Question 18. Can you pass a negative integer as an array size?
Answer:

No, you can’t use a negative number as the size of an array. If you try to do so, an exception will be triggered during runtime.

Question 19. What are the benefits of Heap over Sorted Arrays? 
Answer:

Benefits of Heap over Sorted arrays:

• Heap takes less time complexity as compared to the sorted arrays in terms of creation. Building heap takes O(n) time complexity, whereas building Sorted Array takes O(n.log n) time. 
• Insertion and deletion in the heaps are efficient heaps as compared to sorted arrays. When small numbers of elements are removed or added, with the requirement to print the smallest element after each change, Heap outperforms sorted arrays.
• Multiple heaps can be formed using the same n elements while in sorted arrays, they can be arranged in either ascending or descending order. 

Question 20. Why sparse array is required over simple arrays to store the elements?
Answer:

Sparse arrays are used over simple arrays when the data is sparse, meaning most of the elements are zero or null. They save memory as they only store non-zero elements, reducing space complexity. This makes them efficient for large datasets with lots of empty values.

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