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Data Structure  Interview Questions and Answers for 'Data Structure'  72 question(s) found  Order By Newest  
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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 constanttime 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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Very frequently asked. Favorite question in Walk in Drive of many Indian service companies.  
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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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Advanced level question frequently asked in US based companies. Recently asked in EMC and Intuit.  
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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 (keyaa , value (hashmap(keyaaa,value) b ( key ) > hashmap (keyba , value (hashmap(keybaa,value) .................................................................................... z( key ) > hashmap (keyza , value (hashmap(keyzaa,value) } upto n levels ( where n is the average size of the word in dictionary.  
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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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Ans. First Find the number of nodes in the linked list and take it as n.then find the data at n3 element.  
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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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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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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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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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Ans. http://stackoverflow.com/questions/494830/howtodetermineifalinkedlisthasacycleusingonlytwomemorylocations  
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Ans. BlockingQueue is a Queue that supports operations that wait for the queue to become nonempty when retrieving and removing an element, and wait for space to become available in the queue when adding an element.  
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Ans. [ Open Ended question ]  
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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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Ans. https://qr.ae/TWK2Ok  
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Ans. We can merge two sorted array by using quick sort algorithm  
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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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Ans. Graph contain cycles whereas Trees cannot.  
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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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Ans. public class BinarySearchTree { //Represent the node of binary tree public static class Node { int data; Node left; Node right; public Node(int data) { //Assign data to the new node, set left and right children to null this.data = data; this.left = null; this.right = null; } } //Represent the root of binary tree public Node root; public BinarySearchTree() { root = null; } //factorial() will calculate the factorial of given number public int factorial(int num) { int fact = 1; if (num == 0) return 1; else { while (num > 1) { fact = fact * num; num; } return fact; } } //numOfBST() will calculate the total number of possible BST by calculating Catalan Number for given key public int numOfBST(int key) { int catalanNumber = factorial(2 * key) / (factorial(key 1) * factorial(key)); return catalanNumber; } public static void main(String[] args) { BinarySearchTree bt = new BinarySearchTree(); //Display total number of possible binary search tree with key 5 System.out.println("Total number of possible Binary Search Trees with given key: " bt.numOfBST(5)); } }  
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Ans. list.get(index);  
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Ans. public class StackUsingArrayList { public static void main(String[] args) { List list = new ArrayList(); list.add("A"); list.add("B"); list.add("C"); Stack stack = new Stack(); list.forEach(a > stack.add(a)); System.out.println(stack); } }  
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Ans. Arrays allows elements to be accessed directly using the index. As Array elements are stored in continuous memory locations it's very easy to find the memory address of any element using the formula as following Memory Address of Array start or index 0 + ( Size of array element * Index )  
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