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Here are some important data structures interview questions along with answers:

Practice these questions and get feedbacks! It will help you improve your answer.

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1. How would you find the smallest and largest element in an array?

2. What is the time complexity of enqueue and dequeue operations in a Queue?

3. What is the difference between an Iterator and a ListIterator?

4. How do you handle overflow and underflow conditions in a Queue?

5. What is a stack?

6. What are the basic operations performed on a tree?

7. What are the different types of linked lists?

8. What is the Collections framework?

9. What are the different types of Queues?

10. What is a linked list?

11. What is dynamic programming?

12. How would you reverse an array in-place in linear time and constant space?

13. What is a hash function?

14. Differentiate between directed and undirected graphs.

15. How is a Queue implemented in an array?

16. What are the different ways to represent a tree in memory?

17. How can you convert a binary search tree into a sorted array?

18. What are the operations performed on a stack?

19. What is a graph?

20. What is the difference between a HashMap and a TreeMap?

21. What is the difference between quicksort and mergesort?

22. What is a cycle/loop in Singly Linked List:

23. What is a hash table?

24. What is the time complexity of inserting an element into a heap?

25. What is a heap data structure?

26. When would you choose a tree over other data structures like arrays or linked lists?

27. What is a priority queue?

28. What is an array?

29. Explain the concept of a binary search tree.

30. What is the time complexity for accessing an element in an array?

31. What is the difference between ArrayList and LinkedList?

32. What are the applications of a stack?

33. What are the two types of heaps?

34. Can an array be resized at runtime?

35. Explain Dijkstra’s algorithm and its applications.

36. What is the difference between a Queue and a Stack?

37. Explain different types of trees.

38. What is a circular queue?

39. How do you handle collisions in a hash table?

40. How do you implement a LRU cache?

41. What is the time complexity of deleting an element from a heap?

42. What is a Tree?

43. Describe common graph types.

44. What is a double-ended queue (Deque)?

45. How do you convert a BST into a heap?

46. Why are strings immutable in Java?

47. What is time complexity of Linked List operations?

48. How would you compare Dynamic Arrays Vs Linked Lists?

49. What is a stack overflow?

50. What is a Queue?

51. What is the difference between a HashSet and a TreeSet?

52. How is a Queue implemented in a linked list?

53. What is the difference between a heap and a binary search tree (BST)?

54. What is the time complexity of finding the minimum or maximum element in a heap?

55. Explain the concept of a multi-dimensional array.

56. Describe the different tree traversal methods (preorder, inorder, postorder).

57. What is a hash data structure?

58. What is a stack underflow?

59. What is the time complexity of stack operations?

60. Explain common graph representations.

61. How is a stack implemented in an array?

62. What are the applications of Queues?