100 Must-Know Data Structures Interview Questions and Answers 2024

Arrays and Strings

1.
Explain how you would reverse an array in place.
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2.
What is the difference between an array and a linked list?
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3.
How would you check for duplicates in an array without using extra space?
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4.
Can you explain how to perform a binary search on a sorted array?
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5.
How would you rotate a two-dimensional array by 90 degrees?
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6.
Describe an algorithm to compress a string such as “aabbccc” to “a2b2c3”.
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7.
What is an array slice and how is it implemented in programming languages?
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8.
Can you discuss the time complexity of array insertion and deletion?
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9.
What are some ways to merge two sorted arrays into one sorted array?
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10.
How do you find the kth largest element in an unsorted array?
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Linked Lists

11.
Explain how a singly linked list differs from a doubly linked list.
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12.
How would you detect a cycle in a linked list?
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13.
What are the major operations you can perform on a linked list, and their time complexities?
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14.
Can you describe an in-place algorithm to reverse a linked list?
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15.
Explain how you would find the middle element of a linked list in one pass.
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16.
What are the advantages and disadvantages of using a linked list over an array?
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17.
How can you implement a queue using linked lists?
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18.
Discuss how a linked list can be used to implement a stack.
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19.
How would you remove a given node from a linked list without head pointer?
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20.
Can you explain the concept of a sentinel node in a linked list?
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Stacks and Queues

21.
What operations are performed by a stack data structure?
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22.
How would you evaluate an arithmetic expression using stacks?
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23.
Can you create a queue using two stacks? If so, describe how.
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24.
Describe how you would implement a stack using queues.
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25.
How would you distinguish a stack overflow from an underflow?
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26.
What is a priority queue and how can it be implemented?
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27.
Explain the difference between a LIFO and a FIFO data structure.
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28.
Can you describe a scenario in which a circular queue would be useful?
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29.
How would you design a stack that supports a special operation that retrieves the minimum element in constant time?
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30.
Discuss the potential problems you might encounter when using dynamic arrays for stacks.
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Trees

31.
Describe a binary tree and its properties.
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32.
How do you perform an in-order tree traversal recursively?
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33.
Can you write an algorithm for a non-recursive post-order traversal?
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34.
What are the advantages of a balanced binary tree over an unbalanced one?
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35.
Explain what a binary search tree (BST) is and how it’s different from other trees.
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36.
How would you check if a binary tree is a BST?
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37.
Discuss the method for finding the lowest common ancestor (LCA) in a BST.
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38.
What are the use cases for a depth-first search versus a breadth-first search in a tree structure?
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39.
Describe how you would convert a binary tree into a doubly linked list.
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40.
How can you serialize and deserialize a binary tree?
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Hash Tables

41.
What is a hash table and how does it work internally?
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42.
Can you explain collision resolution in hash tables?
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43.
What is a hash function and what makes a good hash function?
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44.
How would you design a data structure for an LRU cache?
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45.
Discuss the trade-offs between using an array versus a hash table.
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46.
What are some common uses for a hash set data structure?
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47.
How can you count the frequency of words in a long piece of text efficiently?
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48.
What are the implications of a high load factor in a hash table?
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49.
Explain how rehashing works and when it should be performed.
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50.
Discuss the performance differences between hash tables and balanced trees.
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Graphs

51.
Define a graph and its representation in a computer’s memory.
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52.
Explain how you would implement both depth-first search (DFS) and breadth-first search (BFS) on a graph.
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53.
What is the shortest path problem in a graph, and how is it commonly solved?
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54.
Discuss Dijkstra’s algorithm for finding the shortest path.
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55.
Explain what a directed acyclic graph (DAG) is and give an example of where it might be used.
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56.
How would you detect a cycle in a directed graph?
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57.
Discuss the differences between a graph and a tree.
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58.
What is topological sorting and where is it used?
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59.
Can you explain Bellman-Ford’s algorithm and its time complexity?
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60.
How do you determine if a graph is bipartite?
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Sorting and Searching

61.
Describe the quicksort algorithm and its average case time complexity.
Answer:
62.
Explain the difference between a depth-first search and a breadth-first search in a binary tree.
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63.
How would you use a binary search on a rotated sorted array?
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64.
What is the difference between merge sort and heap sort?
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65.
Can you describe bucket sort and give an example of its use case?
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66.
Discuss the advantages of quicksort over other sorting algorithms.
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67.
How does the insertion sort work and what is its time complexity?
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68.
What is a stable sort and why might it be important in certain scenarios?
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69.
Can you explain the counting sort algorithm?
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70.
How would you sort a linked list?
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Advanced Data Structures

71.
Describe a red-black tree and its properties.
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72.
Explain what a B-tree is and where it might be used.
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73.
Discuss the concept of a segment tree and one of its practical applications.
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74.
What is a suffix tree and how is it used in substring search?
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75.
Can you explain what a trie is and when you might use one?
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76.
Discuss the use of a bloom filter and its advantages over a traditional hash table.
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77.
Explain the concept of a disjoint-set and its use in network connectivity.
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78.
What is a Fenwick tree (or binary indexed tree) and when might it be used?
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79.
Discuss the differences between AVL trees and red-black trees.
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80.
How would you implement a rope data structure and what is its use case?
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Design Questions

81.
How would you design a system that requires efficient frequent updates and retrieval of data?
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82.
Discuss how you might implement autocomplete functionality.
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83.
Can you design a data structure that supports insert, delete, get random element operations in constant time?
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84.
Explain how to design a parking lot using object-oriented principles.
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85.
Describe a data structure that could efficiently store a sparse matrix.
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86.
How would you implement a file system directory structure in terms of data structures?
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87.
Discuss the implementation of a phone book which needs to be efficient for look-up, insert, delete, and modification operations.
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88.
Explain the necessary data structures for a text editor which supports insertion, deletion, and character retrieval operations efficiently.
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89.
How would you store a large dataset that allows for efficient range queries and updates?
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90.
Suggest the appropriate data structure for developing a shared document editor that multiple users can edit simultaneously.
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Real-world Applications and Miscellaneous

91.
What data structure would you use for a web browser’s back and forward button implementation?
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92.
Can you create a data structure that dynamically adjusts to user load such that it expands and contracts based on activity?
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93.
Discuss how a data structure can influence database indexing.
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94.
Explain the choice of data structure for implementing a search engine index.
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95.
How would you store and retrieve high-frequency data with minimal latency?
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96.
Discuss the data structures you would use to implement a social network feed.
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97.
How can a leaderboard system in a gaming platform be implemented with regard to data structures?
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98.
Discuss how GPS systems use data structures to find the shortest path effectively.
Answer:
99.
What data structures are involved in the implementation of ride-sharing applications like Uber or Lyft?
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100.
How would a recommendation system benefit from specific data structures to personalize content for users?
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100 Data Structures interview questions

Explain how you would reverse an array in place.

What is the difference between an array and a linked list?

How would you check for duplicates in an array without using extra space?

Can you explain how to perform a binary search on a sorted array?

How would you rotate a two-dimensional array by 90 degrees?

Describe an algorithm to compress a string such as “aabbccc” to “a2b2c3”.

What is an array slice and how is it implemented in programming languages?

Can you discuss the time complexity of array insertion and deletion?

What are some ways to merge two sorted arrays into one sorted array?

How do you find the kth largest element in an unsorted array?

Explain how a singly linked list differs from a doubly linked list.

How would you detect a cycle in a linked list?

What are the major operations you can perform on a linked list, and their time complexities?

Can you describe an in-place algorithm to reverse a linked list?

Explain how you would find the middle element of a linked list in one pass.

What are the advantages and disadvantages of using a linked list over an array?

How can you implement a queue using linked lists?

Discuss how a linked list can be used to implement a stack.

How would you remove a given node from a linked list without head pointer?

Can you explain the concept of a sentinel node in a linked list?

What operations are performed by a stack data structure?

How would you evaluate an arithmetic expression using stacks?

Can you create a queue using two stacks? If so, describe how.

Describe how you would implement a stack using queues.

How would you distinguish a stack overflow from an underflow?

What is a priority queue and how can it be implemented?

Explain the difference between a LIFO and a FIFO data structure.

Can you describe a scenario in which a circular queue would be useful?

How would you design a stack that supports a special operation that retrieves the minimum element in constant time?

Discuss the potential problems you might encounter when using dynamic arrays for stacks.

Describe a binary tree and its properties.

How do you perform an in-order tree traversal recursively?

Can you write an algorithm for a non-recursive post-order traversal?

What are the advantages of a balanced binary tree over an unbalanced one?

Explain what a binary search tree (BST) is and how it’s different from other trees.

How would you check if a binary tree is a BST?

Discuss the method for finding the lowest common ancestor (LCA) in a BST.

What are the use cases for a depth-first search versus a breadth-first search in a tree structure?

Describe how you would convert a binary tree into a doubly linked list.

How can you serialize and deserialize a binary tree?

What is a hash table and how does it work internally?

Can you explain collision resolution in hash tables?

What is a hash function and what makes a good hash function?

How would you design a data structure for an LRU cache?

Discuss the trade-offs between using an array versus a hash table.

What are some common uses for a hash set data structure?

How can you count the frequency of words in a long piece of text efficiently?

What are the implications of a high load factor in a hash table?

Explain how rehashing works and when it should be performed.

Discuss the performance differences between hash tables and balanced trees.

Define a graph and its representation in a computer’s memory.

Explain how you would implement both depth-first search (DFS) and breadth-first search (BFS) on a graph.

What is the shortest path problem in a graph, and how is it commonly solved?

Discuss Dijkstra’s algorithm for finding the shortest path.

Explain what a directed acyclic graph (DAG) is and give an example of where it might be used.

How would you detect a cycle in a directed graph?

Discuss the differences between a graph and a tree.

What is topological sorting and where is it used?

Can you explain Bellman-Ford’s algorithm and its time complexity?

How do you determine if a graph is bipartite?

Describe the quicksort algorithm and its average case time complexity.

Explain the difference between a depth-first search and a breadth-first search in a binary tree.

How would you use a binary search on a rotated sorted array?

What is the difference between merge sort and heap sort?

Can you describe bucket sort and give an example of its use case?

Discuss the advantages of quicksort over other sorting algorithms.

How does the insertion sort work and what is its time complexity?

What is a stable sort and why might it be important in certain scenarios?

Can you explain the counting sort algorithm?

How would you sort a linked list?

Describe a red-black tree and its properties.

Explain what a B-tree is and where it might be used.

Discuss the concept of a segment tree and one of its practical applications.

What is a suffix tree and how is it used in substring search?

Can you explain what a trie is and when you might use one?

Discuss the use of a bloom filter and its advantages over a traditional hash table.

Explain the concept of a disjoint-set and its use in network connectivity.