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Algorithm - Interview Questions and Answers for 'Algorithm' - 62 question(s) found - Order By Newest

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

Q1. Can you provide some implementation of a Dictionary having large number of words ?

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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 (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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Q2. In a Linked list with sorted numbers, insert a new numbers while maintaining the sort order.

^{2017-07-25 14:59:01}

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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Q3. What is the difference between Graph's Breadth first and Depth First algorithm ?

^{2017-07-23 10:12:58}

Ans. In Breadth first algorithm, all the adjacent nodes of the starting node is visited first and then the same rule is followed while moving inwards whereas

In Depth first algorithm, all the nodes of a single traversal path are visited first till a cycle or an end is found.

For example , given the following entries of adjacent nodes

1,2
1,3
1,6
2,4
2,5
3,6

The Breadth first path would be

1,2,3,6,4,5

and Depth first path would be

1,2,4,5,3,6

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Q4. What are the pre-requisite for the collection to perform Binary Search ?

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Ans. 1. Collection should have an index for random access.
2. Collection should have ordered elements.

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Q5. Write an algorithm / Java Program to show duplicates in an array of n elements?

^{2017-01-19 15:37:26}

Ans. int duplicateArray[] = { 1, 2, 2, 3, 4, 5, 6, 8, 9}
Set unique = new HashSet();
for (int i = 0; i < duplicateArray.length; i) {
if (unique.contains(duplicateArray[i])) {
System.out.println(duplicateArray[i]);
} else {
unique.add(duplicateArray[i]);
}
}

Complexity O(n) = nHashSet contains and add has O(n) = 1

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Q6. What is a binary tree ?

^{2017-01-19 15:38:04}

Ans. Binary tree is a tree in which each node has up to two children.Tree is a data structure composed of nodes.Each tree has a root node(not necessary in graph theory). The root node has zero or more child nodes.Each child node has zero or more child nodes, and so on.The tree cannot contain cycles.

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Q7. Write a program for LinkedList, with method to append node and traversing the list ?

^{2017-07-25 14:31:33}

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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Q8. Write a Program for Graph Depth First Traversal using Apache Commons MultiMap

^{2017-07-23 10:01:14}

Ans. import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
import java.util.Set;

import com.google.common.collect.ArrayListMultimap;
import com.google.common.collect.Multimap;

public class Graph {
   private static Multimap<Integer,Integer> adjacentDirectedNodesMap = ArrayListMultimap.create();
   private static Set<Integer> alreadyVisited = new HashSet();

   static{
      adjacentDirectedNodesMap.put(1, 2);
      adjacentDirectedNodesMap.put(1, 3);
      adjacentDirectedNodesMap.put(1, 5);
      adjacentDirectedNodesMap.put(2, 4);
      adjacentDirectedNodesMap.put(4, 5);
   }

   public static void main(String[] args){
      ArrayList visited = new ArrayList();

      Integer startNode = 1;

      displayAdjacentNodes(startNode);

   }

   private static void displayAdjacentNodes(Integer integer){
      if(alreadyVisited.contains(integer)){
         return;
      }
      alreadyVisited.add(integer);
      System.out.println(integer);
      for(Integer adjacentNodes: adjacentDirectedNodesMap.get(integer)){
         displayAdjacentNodes(adjacentNodes);
      }
   }

}

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Q9. Which sorting algorithm is used by Collections.sort() in Java ?

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Ans. The sorting algorithm is a modified mergesort. This algorithm offers guaranteed n log(n) performance.

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Q10. How to determine if the linked list has a cycle in it ?

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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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Q11. Find the repeating number using O(n) time and constant space.

Ans. http://www.geeksforgeeks.org/find-duplicates-in-on-time-and-constant-extra-space/

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Q12. Explain Travelling SalesMan Problem ?

^{2016-11-21 15:21:21}

Ans. https://en.wikipedia.org/wiki/Travelling_salesman_problem

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Q13. Write an Algorithm for Graph Traversal ? The Graph has a loop.

^{2016-11-30 15:42:32}

Ans. Please not that all such questions can be easily answered through recursion.

Simple recursive implementation could be

traverse(root);

void traverse(Element element){
if(element.hasNext()){
traverse(element.next());
} else {
System.out.println(element);
}
}

but this algo / code lead to endless loop if there is a loop in graph traversal.

So you can keep a collection to keep track of which elements have laready been traversed

static List<Elements> listOfAlreadyTraversedElements = new ArrayList<Elements>();

main(){
traverse(root);
}

void traverse(Element element){
if(element.hasNext()){
traverse(element.next());
} else {
listOfAlreadyTraversedElements.add(element);
System.out.println(element);
}
}

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Q14. Flatten a Binary Tree to Linked List

^{2016-12-13 14:49:54}

Ans. https://www.geeksforgeeks.org/flatten-a-binary-tree-into-linked-list/

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Q15. Explain various Searching and Sorting Algorithms ?

^{2017-01-11 16:05:54}

^{This question was recently asked at 'HeadStrong,ServiceNow'.This question is still unanswered. Can you please provide an answer.}

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Q16. Write an algorithm / java program for Heap Sort ?

^{2017-01-19 15:36:18}

Ans. https://www.geeksforgeeks.org/heap-sort/

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Q17. Write any sorting algorithm.

^{2017-01-25 13:41:50}

Ans. https://javasearch.buggybread.com/InterviewQuestions/questionSearch.php?searchOption=label'

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Q18. How to create list that will sort it's elements dynamically?

^{2017-02-21 12:47:22}

Ans. Override the behavior of collection class to sort the list upon each element addition. Though it's not recommended as list are sorting heavy data structures.

List<MyType> list = new ArrayList<MyType>() {
public boolean add(MyType mt) {
super.add(mt);
Collections.sort(list, comparator);
return true;
}
};

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Q19. Write program to create a linked list and perform different operations on it.

^{2017-02-24 14:18:01}

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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Q20. Explain bubble sort.

^{2017-03-03 14:28:51}

Ans. array is traversed from first element to last element. Here current element is compared with next element. If current element is greater than next element it is swapped.

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Q21. Write code to check if a Binary tree is symmetrical

^{2017-03-03 14:29:12}

^{This question was recently asked at 'Amazon'.This question is still unanswered. Can you please provide an answer.}

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Q22. Write a function that returns the depth of a tree.

^{2017-03-03 14:38:46}

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Q23. Write code to find the node where two linked lists intersect.

^{2017-03-03 14:39:39}

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Q24. Check if tic tac toe has a winner

^{2017-03-03 14:40:05}

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Q25. Write program to balance a binary tree

^{2017-03-03 14:40:54}

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Q26. Given a graph, find if it represents a tree

^{2017-03-03 14:41:06}

Ans. We can simply find it by checking the criteria of a tree. A tree will not contain a cycle, so if there is any cycle in the graph, it is not a tree. We can check it using another approach, if the graph is connected and it has V-1 edges, it could be a tree. Here V is the number of vertices in the graph

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Q27. Explain different sorting algorithms and Big O of each

^{2017-03-03 14:41:45}

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Q28. Write a program to find loop in a linked list

^{2017-03-03 14:42:17}

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Q29. How to convert a bst to doubly linked list

^{2017-03-03 14:42:30}

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Q30. How do we implement a weight round robin algorithm in load balancing ?

^{2017-03-19 19:31:41}

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