Hil all below is the question asked to me in my r1 of razorpay , unfortuanelty i recieved rejection mail , even though i thought i belive it went good expect one requirment which i messed up. I believe that might have been the rejection point .
Below is the question and a possible soln that i have built now again .
Your organization has started a new tech blog with interesting tech stories and you’re responsible for designing and implementing an in-memory search engine, supporting the search functionality on the blog content.
Requirements:
package Interviews.Razorpay.Soln.v2;
import java.util.*;
import java.util.stream.Collectors;
// Models
class Blog{
String id;
String raw;
Set<String> words;
Date createdAt;
boolean deleted;
Blog(String text){
if(text.isEmpty() || text.isBlank()) throw new RuntimeException("Cannot provide empty string");
this.raw=text;
this.words=new HashSet<>(List.of(text.split(" ")));
this.createdAt=new Date();
}
void prettyPrint(){
System.out.println("------");
System.out.println("Blog id : "+this.id);
System.out.println("Blog raw text : "+this.raw);
System.out.println("Blog createdAt : "+this.createdAt.toString());
System.out.println("------");
}
}
enum BlogEventType{
BLOG_CREATED,
BLOG_UPDATED,
BLOG_DELETED;
}
class BlogEvent{
final String blogId;
final BlogEventType blogEventType;
final Blog blog;
BlogEvent(String blogId,BlogEventType blogEventType,Blog blog){
this.blogId=blogId;
this.blogEventType=blogEventType;
this.blog=blog;
}
}
// Repositories
class BlogRepository{
private final HashMap<String,Blog> map;
private static BlogRepository instance;
private BlogRepository(){
this.map=new HashMap<>();
}
public static BlogRepository getInstance(){
if(instance==null){
instance=new BlogRepository();
}
return instance;
}
Optional<Blog> findBlogById(String id){
Blog blog= map.getOrDefault(id, null);
if(blog!=null && !blog.deleted) return Optional.of(blog);
else return Optional.empty();
};
Blog updateBlog(String id,Blog updatedBlog){
if(map.containsKey(id) && !map.get(id).deleted){
// update blog
map.put(id,updatedBlog);
return updatedBlog;
}else throw new RuntimeException("Blog with provided id not found");
};
Blog saveBlog(Blog blog){
if(map.containsKey(blog.id)){
throw new RuntimeException("Blog already present");
}else{
blog.id=RandomGenerator.generateRandomId("BLOG-");
map.put(blog.id,blog);
return blog;
}
};
void deleteBlog(String id){
if(map.containsKey(id)){
Blog blog=map.get(id);
blog.deleted= true;
map.put(id,blog);
}else throw new RuntimeException("No blog found with given id");
};
}
// UTILS
class RandomGenerator{
public static String generateRandomId(String prefix){
return prefix+UUID.randomUUID().toString();
}
}
//## Services :
interface BlogEventObserver{
void handleBlogEvent(BlogEvent blogEvent);
}
class BlogService{
List<BlogEventObserver> observers;
BlogRepository blogRepository;
BlogService(BlogRepository blogRepository){
this.blogRepository=blogRepository;
observers=new ArrayList<>();
}
Blog addBlog(Blog blog){
Blog createdBlog=blogRepository.saveBlog(blog);
BlogEvent blogEvent=new BlogEvent(createdBlog.id,BlogEventType.BLOG_CREATED,createdBlog);
notifyObservers(blogEvent);
return createdBlog;
}
Optional<Blog> getBlogById(String id){
return blogRepository.findBlogById(id);
}
Blog updateBlog(String id ,Blog blog){
Blog updatedBlog= blogRepository.updateBlog(id,blog);
notifyObservers(new BlogEvent(
id,BlogEventType.BLOG_UPDATED,updatedBlog
));
return updatedBlog;
}
void deleteBlog(String id){
Blog blog=blogRepository.findBlogById(id).get();
blogRepository.deleteBlog(id);
notifyObservers(new BlogEvent(
id,BlogEventType.BLOG_DELETED,blog
));
}
void notifyObservers(BlogEvent blogEvent){
observers.forEach(observer->observer.handleBlogEvent(
blogEvent
));
}
BlogEventObserver addObserver(BlogEventObserver observer){
if(!observers.contains(observer)){
observers.add(observer);
}
return observer;
}
void removeObserver(BlogEventObserver observer){
observers.remove(observer);
}
}
interface SortStrategy {
List<Blog> sort(List<Blog> blogs);
}
class SortByCreatedDate implements SortStrategy{
@Override
public List<Blog> sort(List<Blog> blogs) {
List<Blog> sortedList=new ArrayList<>(blogs);
sortedList.sort(Comparator.comparing(a -> a.createdAt));
return sortedList;
}
}
class SearchService implements BlogEventObserver{
HashMap<String,Set<String>> wordIdsMap;
BlogService blogService;
SortStrategy sortStrategy;
SearchService(BlogService blogService){
this.blogService=blogService;
this.sortStrategy = new SortByCreatedDate();
wordIdsMap=new HashMap<>();
}
private void insertBlog(String blogId) {
Blog blog=blogService.getBlogById(blogId).get();
List<String> words= List.of(blog.raw.split(" "));
for(String word: words){
if(word.isBlank() || word.isEmpty()) continue;
Set<String> ids=wordIdsMap.getOrDefault(word,new HashSet<>());
ids.add(blog.id);
wordIdsMap.put(word,ids);
}
}
private void deleteBlog(Blog blog) {
List<String> words= List.of(blog.raw.split(" "));
for(String word: words){
if(word.isBlank() || word.isEmpty()) continue;
Set<String> ids=wordIdsMap.getOrDefault(word,new HashSet<>());
ids.remove(blog.id);
wordIdsMap.put(word,ids);
}
}
private void updateBlog(String blogId) {
Blog blog=blogService.getBlogById(blogId).get();
// can improve the approach but for now going with naive
HashMap<String,HashSet<String>> updatedMap=new HashMap<>();
for(String key: wordIdsMap.keySet()){
Set<String> ids=wordIdsMap.get(key);
ids.remove(blog.id);
wordIdsMap.put(key,ids);
}
}
public void setSortStrategy(SortStrategy sortStrategy){
this.sortStrategy=sortStrategy;
}
public List<Blog> searchBlog(List<String> keywords){
// base case
if(keywords.isEmpty()) return new ArrayList<>();
Set<String> resultBlogIds=new HashSet<>(wordIdsMap.get(keywords.get(0)));
if(resultBlogIds.isEmpty()) return new ArrayList<>();
// keep eliminating blog ids which doesn't contain all the words
for(int i=1;i<keywords.size() && !resultBlogIds.isEmpty();i++){
String keyword=keywords.get(i);
// if word is not present simply return empty list
if(!wordIdsMap.containsKey(keyword)) return new ArrayList<>();
Set<String> idList=wordIdsMap.get(keyword);
// keep filtering blog ids
Set<String> updatedIds=new HashSet<>();
resultBlogIds.forEach(id->{
if(idList.contains(id))
updatedIds.add(id);
});
resultBlogIds=updatedIds;
}
List<Blog> results=resultBlogIds.stream()
.map(blogId->blogService.getBlogById(blogId))
.filter(Optional::isPresent)
.map(Optional::get)
.collect(Collectors.toList());
return sortStrategy.sort(results);
}
List<Blog>searchBlog(String input){
if(input==null || input.isEmpty() || input.isBlank()) throw new RuntimeException("invalid search key provided ");
return searchBlog(List.of(input.split(" ")));
}
@Override
public void handleBlogEvent(BlogEvent blogEvent) {
BlogEventType event=blogEvent.blogEventType;
String blogId=blogEvent.blogId;
Blog blog=blogEvent.blog;
// update blog in search map
if(event.equals(BlogEventType.BLOG_CREATED)){
System.out.println("processing blog in word map");
insertBlog(blogId);
}
else if(event.equals(BlogEventType.BLOG_UPDATED)){
System.out.println("updating blog in word map");
updateBlog(blogId);
}
else if(event.equals(BlogEventType.BLOG_DELETED)){
System.out.println("deleting blog in word map");
deleteBlog(blog);
}
}
}
public class Test {
public static void main(String[] args) {
BlogRepository blogRepository= BlogRepository.getInstance();
BlogService blogService=new BlogService(blogRepository);
SearchService searchService=new SearchService(blogService);
// add search service as observer for any events happening to blog service
blogService.addObserver(searchService);
Blog blog1=new Blog("AI IS EVERYWHERE ");
blogService.addBlog(blog1);
Blog blog2=new Blog("AI WILL KILL EVERYWHERE JOB");
blogService.addBlog(blog2);
Blog blog3=new Blog("AI IS CHUTIYA");
blogService.addBlog(blog3);
System.out.println("------ TEST CASE - 1 ------");
searchService.searchBlog("AI")
.forEach(Blog::prettyPrint); ;// should print all above 3 in ordered way by creation date
System.out.println("------ TEST CASE - 2 ------");
searchService.searchBlog("AI EVERYWHERE ")
.forEach(Blog::prettyPrint); ;// should print only 2 blog 1,2 results in ordered way by creation date
blogService.deleteBlog(blog2.id);
System.out.println("------ TEST CASE - 3 ------");
searchService.searchBlog("AI EVERYWHERE ")
.forEach(Blog::prettyPrint); ;// should print only 1 result blog 1 in ordered way by creation date
System.out.println("------ TEST CASE - 4 ------");
searchService.searchBlog("AI IS ")
.forEach(Blog::prettyPrint); ;// should print only 2 result blog 1 ,3 in ordered way by creation date
Blog blog4=new Blog("MGRS ARE NAZI");
blogService.addBlog(blog4);
Blog blog5=new Blog("ALL MGRS ARE WORTHLESS");
blogService.addBlog(blog5);
System.out.println("------ TEST CASE - 5 ------");
searchService.searchBlog("MGRS")
.forEach(Blog::prettyPrint); ;// should print only 2 result blog 4,5 in ordered way by creation date
blogService.deleteBlog(blog5.id);
System.out.println("------ TEST CASE - 6 ------");
searchService.searchBlog("MGRS")
.forEach(Blog::prettyPrint); ;// should print only 1 result blog 4 in ordered way by creation date
System.out.println("------ TEST CASE - 7 ------");
searchService.setSortStrategy((list)->
list.stream().sorted(Comparator.comparing(a->a.raw)).toList()
); // functional interface approach sorting based on text lexicographically
searchService.searchBlog("AI")
.forEach(Blog::prettyPrint); ;// should print only result blog 1,3 in ordered way by creation date
/*
* Using observer pattern for notifying search service for change in blog from blog service
Using singleton pattern to replicate the single db instance ( blog repository case )
Using strategy pattern to sort the search results based on the given strategy
* */
}
}Below is the output which i am gettting
processing blog in word map
processing blog in word map
processing blog in word map
------ TEST CASE - 1 ------
------
Blog id : BLOG-a596df3c-94a3-46bb-8a01-f93e9cc23d4d
Blog raw text : AI IS EVERYWHERE
Blog createdAt : Sun Oct 27 20:12:01 IST 2024
------
------
Blog id : BLOG-d509dd0a-4429-440b-829a-65c6ad1370fe
Blog raw text : AI IS CHUTIYA
Blog createdAt : Sun Oct 27 20:12:01 IST 2024
------
------
Blog id : BLOG-4af57a01-913e-46eb-9d26-90192a7f05b8
Blog raw text : AI WILL KILL EVERYWHERE JOB
Blog createdAt : Sun Oct 27 20:12:01 IST 2024
------
------ TEST CASE - 2 ------
------
Blog id : BLOG-a596df3c-94a3-46bb-8a01-f93e9cc23d4d
Blog raw text : AI IS EVERYWHERE
Blog createdAt : Sun Oct 27 20:12:01 IST 2024
------
------
Blog id : BLOG-4af57a01-913e-46eb-9d26-90192a7f05b8
Blog raw text : AI WILL KILL EVERYWHERE JOB
Blog createdAt : Sun Oct 27 20:12:01 IST 2024
------
deleting blog in word map
------ TEST CASE - 3 ------
------
Blog id : BLOG-a596df3c-94a3-46bb-8a01-f93e9cc23d4d
Blog raw text : AI IS EVERYWHERE
Blog createdAt : Sun Oct 27 20:12:01 IST 2024
------
------ TEST CASE - 4 ------
------
Blog id : BLOG-a596df3c-94a3-46bb-8a01-f93e9cc23d4d
Blog raw text : AI IS EVERYWHERE
Blog createdAt : Sun Oct 27 20:12:01 IST 2024
------
------
Blog id : BLOG-d509dd0a-4429-440b-829a-65c6ad1370fe
Blog raw text : AI IS CHUTIYA
Blog createdAt : Sun Oct 27 20:12:01 IST 2024
------
processing blog in word map
processing blog in word map
------ TEST CASE - 5 ------
------
Blog id : BLOG-4e427560-392b-4952-ab6d-6317d10cbd08
Blog raw text : ALL MGRS ARE WORTHLESS
Blog createdAt : Sun Oct 27 20:12:01 IST 2024
------
------
Blog id : BLOG-1cfd81ca-9e81-4f40-9cbe-30d2f77fb48f
Blog raw text : MGRS ARE NAZI
Blog createdAt : Sun Oct 27 20:12:01 IST 2024
------
deleting blog in word map
------ TEST CASE - 6 ------
------
Blog id : BLOG-1cfd81ca-9e81-4f40-9cbe-30d2f77fb48f
Blog raw text : MGRS ARE NAZI
Blog createdAt : Sun Oct 27 20:12:01 IST 2024
------
------ TEST CASE - 7 ------
------
Blog id : BLOG-d509dd0a-4429-440b-829a-65c6ad1370fe
Blog raw text : AI IS CHUTIYA
Blog createdAt : Sun Oct 27 20:12:01 IST 2024
------
------
Blog id : BLOG-a596df3c-94a3-46bb-8a01-f93e9cc23d4d
Blog raw text : AI IS EVERYWHERE
Blog createdAt : Sun Oct 27 20:12:01 IST 2024
------Hope it helps the community . Please provide any feedback in comments for which part i can approve.
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