Data Structure - Interview Questions and Answers for 'Data structure' | Search Interview Question

Data Structure - Interview Questions and Answers for 'Data structure' - 74 question(s) found - Order By Newest

Very frequently asked. Favorite question in Walk in Drive of many Indian service companies.

Q1. What is the difference between ArrayList and LinkedList ?

Ans. Underlying data structure for ArrayList is Array whereas LinkedList is the linked list and hence have following differences -

1. ArrayList needs continuous memory locations and hence need to be moved to a bigger space if new elements are to be added to a filled array which is not required for LinkedList.

2. Removal and Insertion at specific place in ArrayList requires moving all elements and hence leads to O(n) insertions and removal whereas its constant O(1) for LinkedList.

3. Random access using index in ArrayList is faster than LinkedList which requires traversing the complete list through references.

4. Though Linear Search takes Similar Time for both, Binary Search using LinkedList requires creating new Model called Binary Search Tree which is slower but offers constant time insertion and deletion.

5. For a set of integers you want to sort using quicksort, it's probably faster to use an array; for a set of large structures you want to sort using selection sort, a linked list will be faster.

Sample Code for ArrayList

Sample Code for LinkedList

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Frequently asked.

Q2. If you are given a choice to use either ArrayList and LinkedList, Which one would you use and Why ?

Core Java

Ans. ArrayList are implemented in memory as arrays and hence allows fast retrieval through indices but are costly if new elements are to be inserted in between other elements. LinkedList allows for constant-time insertions or removals using iterators, but only sequential access of elements

1. Retrieval - If Elements are to be retrieved sequentially only, Linked List is preferred.

2. Insertion - If new Elements are to be inserted in between other elements , Linked List is preferred.

3. Search - Binary Search and other optimized way of searching is not possible on Linked List.

4. Sorting - Initial sorting could be pain but lateral addition of elements in a sorted list is good with linked list.

5. Adding Elements - If sufficiently large elements needs to be added very frequently ,Linked List is preferable as elements don't need consecutive memory location.

Sample Code for ArrayList

Sample Code for LinkedList

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Advanced level question frequently asked in US based companies. Recently asked in EMC and Intuit.

Q3. Can you provide some implementation of a Dictionary having large number of words ?

Solution

Ans. Simplest implementation we can have is a List wherein we can place ordered words and hence can perform Binary Search.

Other implementation with better search performance is to use HashMap with key as first character of the word and value as a LinkedList.

Further level up, we can have linked Hashmaps like ,

hashmap {
a ( key ) -> hashmap (key-aa , value (hashmap(key-aaa,value)
b ( key ) -> hashmap (key-ba , value (hashmap(key-baa,value)
....................................................................................
z( key ) -> hashmap (key-za , value (hashmap(key-zaa,value)
}

upto n levels ( where n is the average size of the word in dictionary.

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Q4. In a Linked list with sorted numbers, insert a new numbers while maintaining the sort order.

Algorithm

Ans.
public class LinkedList {

   Node start = null;
   Node head = null;

   class Node{
      Integer body;
      Node nextNode;

      Node(Integer value){
         body = value;
      }
   }

   private void insertInMiddle(Integer value){
      head = start;
      if(start == null) {
         start = new Node(value);
         head = start;
         head.nextNode = null;
         return;
      }

      while(head.body < value){
         if(head.nextNode == null || head.nextNode.body >= value){
            Node newNode = new Node(value);
            newNode.nextNode = head.nextNode;
            head.nextNode = newNode;

            break;
         }
         head = head.nextNode;
      }
   }

   private void traverse(){
      head = start;
      while(head != null){
         System.out.println(head.body);
         head = head.nextNode;
      }
   }

   public static void main(String[] args){
      LinkedList ll = new LinkedList();

      ll.insertInMiddle(5);
      ll.insertInMiddle(10);
      ll.insertInMiddle(15);
      ll.insertInMiddle(7);

      ll.traverse();

   }
}

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Q5. What is a BlockingQueue?

Data Structures

Ans. BlockingQueue is a Queue that supports operations that wait for the queue to become non-empty when retrieving and removing an element, and wait for space to become available in the queue when adding an element.

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Q6. Design a Data Structure for a full text Search ?

Design

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Q7. Write a Program to reverse a Linked List ?

Data Structure

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Q8. Find the third last element in a linked list ?

Data Structure

Ans. First Find the number of nodes in the linked list and take it as n.then find the data at n-3 element.

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Q9. Write a program for LinkedList, with method to append node and traversing the list ?

Algorithm

Ans. public class LinkedList {

   Node start = null;
   Node head = null;

   class Node {
      Integer body;
      Node nextNode;

      Node(Integer value) {
         body = value;
      }
   }

   private void addNodeToEnd(Integer value) {
      if (start == null) {
         start = new Node(value);
         head = start;
         head.nextNode = null;
         return;
      }

      while (head.nextNode != null) {
         head = head.nextNode;
      }

      head.nextNode = new Node(value);
   }

   private void traverse() {
      head = start;
      while (head != null) {
         System.out.println(head.body);
         head = head.nextNode;
      }
   }

   public static void main(String[] args) {
      LinkedList ll = new LinkedList();

      ll.addNodeToEnd(5);
      ll.addNodeToEnd(10);
      ll.addNodeToEnd(15);

      ll.traverse();

   }
}

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Q10. Write method to delete Node from a LinkedList.

Data Structure

Ans. public class LinkedList {

   Node start = null;
   Node head = null;

   class Node {
      Integer body;
      Node nextNode;

      Node(Integer value) {
         body = value;
      }
   }

   private void addNodeToEnd(Integer value) {
      if (start == null) {
         start = new Node(value);
         head = start;
         head.nextNode = null;
         return;
      }

      while (head.nextNode != null) {
         head = head.nextNode;
      }

      head.nextNode = new Node(value);
   }

   private void deleteNode(Integer value) {
      head = start;
      while (head.nextNode != null) {
         if(head.nextNode.body == value){
            head.nextNode = head.nextNode.nextNode;
         }

         head = head.nextNode;
      }
   }



   private void traverse() {
      head = start;
      while (head != null) {
         System.out.println(head.body);
         head = head.nextNode;
      }
   }

   public static void main(String[] args) {
      LinkedList ll = new LinkedList();

      ll.addNodeToEnd(5);
      ll.addNodeToEnd(10);
      ll.addNodeToEnd(15);

      ll.traverse();

      ll.deleteNode(10);

      ll.traverse();

   }
}

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Q11. What is the difference between pop and peek function of stack ?

Data Structure

Ans. pop method pulls the top element from the stack and then move the top to the next element whereas peek only get the top element but doesn't move the top.

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Q12. What is the difference between Data Type and Data Structure ?

Core Java

Ans. Data type: a set of values together with operations on that type
Data structure: a physical implementation of a data type

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Q13. Do you see Class as a Data Type or Data Structure ?

Ans. Class can be better seen as Data Type. This could be implemented as a Data Structure too in some cases.

One thing worth understanding here is that Data type and Data structure are conceptual things. Class could be implementation of either of these.

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Q14. How to determine if the linked list has a cycle in it ?

Ans. http://stackoverflow.com/questions/494830/how-to-determine-if-a-linked-list-has-a-cycle-using-only-two-memory-locations

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Q15. Which Data Structure should be used for Load Balancer ?

Ans. [ Open Ended question ]

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Q16. Explain what happens when insertion is performed in case of ArrayList and LinkedList.

Data Structure

Ans. Array List works on Array and when we add an element in middle of the list, Array List need to update the index of all subsequent elements. I the capacity is full, it even may need to move the whole list to a new memory location . Linked List works on Double linked list algorithm and all it has to do is to adjust the address of the previous and next elements.

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Q17. What is the difference between circular queue and priority queue ?

Data Structures

Ans. https://qr.ae/TWK2Ok

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Q18. Write program to create a linked list and perform different operations on it.

Algorithm

Ans. import java.util.*;
class LinkedListSolution{
protected LinkedList list;
public LinkedListSolution(){
list = new LinkedList();
}
public Object pop() throws NoSuchElementException{
if(list.isEmpty())
throw new NoSuchElementException();
else
return list.removeFirst();
}
public void push(Object obj){
list.addFirst(obj);
}
public Object peek() throws NoSuchElementException{
if(list.isEmpty())
throw new NoSuchElementException();
else
return list.getFirst();
}
public boolean isEmpty(){
return list.isEmpty();
}
public String toString(){
return list.toString();
}
}
class TestStack{
public static void main(String args[]){
LinkedListSolution s = new LinkedListSolution();
s.push("First");
s.push("Second");
s.push("Third");
System.out.println("Top: " s.peek());
s.push("Fourth");
while(!(s.isEmpty()))
System.out.println(s.pop());
}
}

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Q19. Write a Program to delete a node from Linked List ?

Data Structure

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Q20. What data structure will you use if we have to search an element in million of elements ?

Data Structure

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Q21. Write a Program to find the middle element of Linked List ?

Data Structure

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Q22. Write a Program to merge two sorted arrays ?

Data Structure

Ans. We can merge two sorted array by using quick sort algorithm

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Q23. Implement stack using generics in Java.

Data Structure

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Q24. How to implement a hashtable ?

Data Structure

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Q25. What is the difference between Stack and Queue ?

Data Structures

Ans. Stack is based on Last in First out (LIFO) principle while a queue is based on FIFO (First In First Out) principle.

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Q26. Difference between Tree and Graph ?

Data Structures

Ans. Graph contain cycles whereas Trees cannot.

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Q27. Write a Program to implement stack using LinkedList.

Data Structure

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Q28. Describe how you could use a single array to implement three stacks

Algorithm

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Q29. Write a program to sort a stack in ascending order You should not make any assumptions about how the stack is implemented The following are the only functions that should be used to write this program: push | pop | peek | isEmpty

Algorithm

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Q30. In a Tree, find common ancestor of two nodes.

Data Structures

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