List of 200 Data Structures Interview Questions

Data structures are the fundamental building blocks of computer science and software development. They are essential for efficiently organizing and managing data in computer programs. Whether you’re a job seeker preparing for a technical interview or a student studying data structures, mastering these concepts is crucial.

In this article, we’ve compiled 200 data structures interview questions to help you understand and practice these important topics.

1. What is an abstract data type?
2. What abstract data type would be used to store a whole number?
3. Explain how a memory address is used to access an abstract data type that is larger than 1 byte.
4. What is the difference between a float abstract data type and a double abstract data type?
5. What is precision?
6. Explain how memory is organized within a computer.
7. What is a numbering system?
8. Why is the binary numbering system used in computing?
9. Why don’t you directly specify the number of bytes to reserve in memory to store data?
10. Explain the impact signed and unsigned numbers have on memory.
11. What is a user-defined data type?
12. How do you determine the size of a structure?
13. Why would you use a structure?
14. Why happens when you declare an instance of a structure?
15. How do you access parts of a structure?
16. What is a pointer?
17. Why would you use a pointer in a program?
18. What is a pointer to a pointer?
19. Why would you use a pointer to a pointer in a program?
20. What is shown on the screen if you display the content of a pointer variable?
21. What is the difference between an array element and a variable?
22. What is an array of pointers?
23. How do you assign an address to an element of a pointer array?
24. What is an array of pointers to pointers?
25. How do you assign a value to an element of an array of pointers to pointers?
26. How do you display the contents of the memory addresses stored in an element of a pointer array?
27. Why would you use an array of pointers to pointers?
28. How do you declare an array?
29. How do you display the contents of the memory addresses stored in an element of an array of pointers to pointers?
30. How are elements of an array stored in memory?
31. What is a stack?
32. What is the purpose of the push() member method?
33. What is the purpose of the pop() member method?
34. What is the purpose of the isFull() member method?
35. What is the purpose of the isEmpty() member method?
36. What kind of value is assigned to the top attribute?
37. Why is the top attribute initialized to –1?
38. What is the purpose of the keyword private?
39. What is the purpose of the keyword public?
40. What is the difference between a constructor and a destructor?
41. What is a queue?
42. What is the relationship between a queue and its underlying array?
43. Explain how the index of the front and back of the queue is calculated.
44. What is the purpose of the enqueue process?
45. What is the purpose of the dequeue process?
46. Why is the isFull() member method called?
47. Why is the isEmpty() member method called?
48. What happens to the data stored on the array when the data is removed from the queue?
49. What is the purpose of setting the default size of the queue?
50. Why does the C++ version of the queue delete the underlying array from memory using the destructor and the Java version of the queue does not?
51. What is a linked list?
52. What is the benefit of using a linked list?
53. What is a node?
54. What are the elements of a node?
55. What advantage does a linked list have over an array?
56. Can a node reference more than one data element?
57. In Java, why can’t you pass a primitive data type to the add() method of the LinkedList class?
58. How can a node be inserted in the middle of a linked list?
59. What is a doubly linked list?
60. What is a single linked list?
61. What is a stack-linked list?
62. How does a stack-linked list differ from a linked list?
63. What is the benefit of using a stack-linked list?
64. Where is the front of the stack in a stack-linked list?
65. What is the maximum number of nodes that you can have on a stack-linked list?
66. Can a node on a stack-linked list have more than one data element?
67. Why does the StackLinkedList class inherit the LinkedList class?
68. Why is the constructor of the StackLinkedList class empty?
69. Why is the destructor of the StackLinkedList class empty?
70. What happens when you push a new node onto a stack?
71. What is a queue linked list?
72. How does a queue linked list differ from an array queue?
73. What is the benefit of using a queue linked list?
74. Where are new nodes added to the queue?
75. Which node is removed from the queue when the dequeue() member method is called?
76. Can a node on a queue linked list have more than one data element?
77. What form of access is used to add and remove nodes from a queue?
78. Why is the constructor of the QueueLinkedList class empty?
79. Why does the QueueLinkedList class inherit the LinkedList class?
80. What happens when dequeue() is called?
81. What is a linked list index?
82. What is the value of the first linked list index?
83. What is the difference between the removeNode() and deleteNode() functions?
84. What is the return value of the findNode() function?
85. What is the difference between the insertNodeAt()and the appendNode() functions?
86. What happens if an invalid index value is passed to a function?
87. Can a linked list store data other than integers?
88. Why would you define a getSize() function instead of having the application access the size of the linked list directly?
89. Can the insertNodeAt() function place a node at the front or back of a linked list?
90. Why is it important to enhance the functionality of the LinkedList class?
91. What is a tree?
92. What is the relationship between parent node and child nodes?
93. What are a key and a value?
94. What is a root node?
95. What is the purpose of a left child node and a right child node?
96. What is a leaf node?
97. What is the depth of a tree?
98. What is the size of a tree?
99. How do you calculate the size of a tree?
100. Can a tree have a duplicate key?
101. What is hashing?
102. Why is it necessary to hash?
103. What is a hashtable?
104. What is the result of hashing?
105. How is a key hashed?
106. Can a key entered by an application be directly compared to a key in a hashtable?
107. What programming technique is used for hashing in all hashing functions?
108. Why are data members of the Hashtable class stored in the private access specifier?
109. At what level is hashing performed?
110. Is there one hashing function used in all applications for hashing?
111. What is the binary numbering system?
112. What is the purpose of an abstract data type?
113. What is a variable?
114. What is the integer abstract data type group?
115. What does the term “floating-point” mean?
116. What is a character?
117. What is the difference between single and double precision?
118. What is an instance of a structure?
119. What kind of data type is a structure?
120. How do you reference an element of an instance of a structure?
121. What are three major elements of every class definition?
122. What is the difference between a class definition and a structure definition?
123. What is the hexadecimal numbering system?
124. How do you assign an address to a pointer?
125. What value is stored in a pointer variable?
126. Why do you use pointer arithmetic?
127. What is a pointer-to-pointer variable?
128. What is an array of elements?
129. What is an index?
130. What is a multidimensional array?
131. What is the purpose of using a multidimensional array?
132. What is the relationship between a pointer and an array?
133. What is the relationship between a stack and an array?
134. What is the action called that places data on a stack?
135. What is the action called that removes data from a stack?
136. Using an array, how do you determine whether the stack is empty?
137. Using an array, how do you determine whether the stack is full?
138. Where is data organized in a queue stored?
139. What does the term “circular queue” mean?
140. What is the modulus operator used for with respect to circular queues?
141. When would you implement a queue using a linked list instead of an array?
142. What is the action called that places data on a queue?
143. What is the action called that removes data from a queue?
144. What is an entry in a linked list called?
145. How are nodes linked together in a linked list?
146. What is the purpose of a doubly linked list?
147. What is used to define a node of a linked list?
148. How do you delete an element from the middle of a linked list?
149. How do you delete a node from the front of a linked list?
150. How do you append a node onto a linked list?
151. How do you put a new node onto the front of the linked list?
152. What condition tells you the linked list is currently empty?
153. What condition tells you there’s only one node on the linked list?
154. What is the size limitation on a linked list?
155. What is the destructor typically used for in a linked list?
156. What is the key used for in a hashtable?
157. What is the significance of a hash value?
158. What major problem occurs with hashing?
159. How do you overcome the major problem that occurs with hashing?
160. Ideally, how should a hash function behave with respect to the values it generates? If you feed in a list of keys, what would you expect for the output?
161. Many different hashing algorithms have been developed to provide a more even distribution of hash values. What is the essence of the hashing algorithm—in other words, what do these functions typically have in common?
162. With a hashtable, suppose your dataset gets unexpectedly large and you have an excessive number of collisions. How could you deal with this?
163. How do you insert a node into a hashtable?
164. How do you delete a node from a hashtable?
165. How do you look up a value in a hashtable?
166. How do you list out all the values in a hashtable?
167. How would you check if a hashtable is empty?
168. What is a binary tree?
169. What is the purpose of a branch node in a binary tree?
170. What is the starting node of a binary tree called?
171. What is the node in a binary tree called that spawns another node?
172. What are nodes at the end of a binary tree called?
173. If you have 1,000 nodes in a balanced binary tree, approximately how many comparisons do you need to do to find a particular node?
174. How is the maximum depth of a tree defined?
175. If a binary tree is well balanced, approximately how many nodes are in the tree given the depth of the tree?
176. What condition do you check for to see if a node in a binary tree is a leaf node?
177. How do you delete a node from a binary tree that has two child nodes?
178. How do you delete a node from the binary tree that has one child node?
179. How do you delete a leaf node from a binary tree?
180. What is the basic rule for where the nodes get placed into a binary tree?
181. How do you insert a node into a binary tree?
182. How would you check if a binary tree is empty?
183. What is a recursive function?
184. When searching for a key in a binary tree, what stops the recursive function calls?
185. What is the sequence of function calls to do an “in order” traversal of a binary tree?
186. What is memory allocation?
187. What does the new operator return?
188. Does Java use pointers?
189. How do you declare an array of pointers?
190. How do you declare an array of pointers to pointers?
191. If an int pointer is incremented using pointer arithmetic, how many bytes is the pointer incremented?
192. How is a binary tree’s depth defined?
193. What is a balanced binary tree?
194. Must all binary trees be balanced?
195. What is the purpose of a key in a binary tree?
196. What is metadata?
197. What is the purpose of the this operator?
198. What does a private access specifier do?
199. What is fifo?
200. What is the purpose of a public access specifier?

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