Reverse a String - Java Interview Coding Challenge #3 [Java Brains]

[@Java.Brains]

Thanks for all the great comments: Couple of things: 1. Yes, using character array is an option. You can use that instead of StringBuffer to save from creating a gazillion strings 2. Don't go for recursion unless asked. My suggestion is to mentally evaluate which is the simpler option. Recursion adds a cognitive load to whoever will read code in the future. So, use it only if it makes the solution simpler and more elegant than the iterative approach.

[@lxerlx2890]

A straightforward implementation iterating through individual characters of the string will fail if the string contains an Unicode supplementary character (with code points U+10000 to U+10FFFF), which is encoded as a pair of _char_ values in Java. The implementation with *StringBuilder(str).reverse().toString()* should be preferred because it will work even if the string has an Unicode supplementary character. One can see the difference between two methods by trying with the string "s𝕋u" which contains a supplementary character (U+1D54B) in the middle of the string. Because all of these, it is not recommended to use _char_ type in the programs unless the intent is to actually manipulate UTF-16 code units.

[@etric89]

1. char[] chars = str.toCharArray(). 2. Traverse chars[] array from 0 to n/2 swapping elements from first half with ones from second: chars[idx] chars[n-1-idx]. 3. Create new string: new String(chars).

[@soumyajitdey5720]

Exactly what I had in mind

[@antmakov]

You can actually set character individually in a string by calling setCharAt(int index, char c) function and you basically don't need to create char [] array

[@etric89]

@@antmakov java.lang.String is an immutable class

[@antmakov]

@@etric89 my bad, setCharAt exists only in string builder class not in string. And as you mentioned it's pointless to set character on string if it's immutable.

[@AjinkyaRane]

Hey Koushik nice way to explain. simultaneous explanation on writing pad is helping to understand concepts quickly. I would request you to do video on 1. String pool & immutability. Diff new String() & String literal 2. Writing immutable classes. 3. Internal working of HashMap 4. Dutch National Flag problem. If these are already in pipeline..👍

[@PramriDesigns]

One thing I always remember your one line u mention in first SOAP Sample program "Writing a SOAP web services is very difficult, so Please pay attention to that then when you write @webservice then u said job done. then u mention that u were just kidding :) then I watch your all SOAP videos in 2 days and learned complete concept within 2 days. " I always remember this line :)

[@dhanushkakumarage1889]

Hes also kidding with angular series.. quantum physics and relativity 😁😁😁

[@phanindraitika5609]

Just another thought... we can loop thru the string and instead of appending it to another string...store each character in a character array and at the end create one new string with the character array... Also I believe to test our Java 8 features knowledge, interviewers may ask a solution using lambda expression...!! Good one... A pretty good refresher... These days I need a dose of your videos daily 😄 keep doing good work .. thanks for the videos again !!

[@tusharkshirsagar611]

You are not just teacher, but an incredible teacher... Thanks Kaushik...!!!

[@edgieacepojadas6700]

Back in my college days, all I did with this kind of problem is that I just put the string on an array and call the array in reverse, well I don't know if it's efficient thou, but it works and got some grade for it. lol

[@uma_r]

I know one person with 8+ years of experience, when asked this question, left the interview hall saying it's too basic.

[@Java.Brains]

This is probably not a good interview question for someone with 8 years of experience. Having said that, the important thing is not the question itself- it’s the discussions around it. I’d ask the experienced candidate to explore time and space complexities with extremely large data sets. Example: what if the incoming string is larger than the available memory capacity? There are tons of opportunities to explore complexity even in the simplest of interview questions. :)

[@uma_r]

@@Java.Brains wonderful. I never had such thoughts :)

[@amirthasaha]

Thank you very much Koushik sir. you just rock in your teaching style. Please make courses on Core java concepts, Design patterns, Data Structure/Algorithms sir. Java Brains will become one stop for every Java Programmer from the beginner till whatever is the highest level. Thank you so so much sir.

[@pushpesh82]

I would love to see this series going for solving 50 such questions...

[@sebastianmendoza2005]

Nice explanation. Some other ways I think this could be done is recurssion going from both ends to the center O(n/2). Another really easy way is to just use a stack, it would automatically return anything in it in reverse order once it is emptied.

[@vivekbhadauria2130]

Infact this recursion based approach helps in dynamic programming problems related to palindromic strings

[@sleepy_Dragon]

Did you check if this is working with upper Unicode characters? I think one would have to use code points. Otherwise emoticons and such would break.

[@nikhilraut6820]

For life -abdul kalam ji....for java- Kaushik ji...salute both of u.... thanks make me better 😊🙏

[@arunabhhejib1136]

Hi Kaushik, how about making videos on currently hot topics like Kafka, Rabbit MQ, Cassandra. Messaging frameworks and NoSQL databases? That would be really helpful. Thanks!

[@howtoed3116]

We could also have reduced the complexity by interchanging value at 0 to value at n-1, and then doing the same for all chars till I=n/2.

[@wiper123ful]

Hi Koushik, Can you do a video on hash map implementation??

[@asankaishara]

This method can do it with O(n/2) complexity. Else it will be O(n) private static String reverseString(String s) { char[] charArray = s.toCharArray(); int start = 0; int end = charArray.length - 1; while (start

[@uppunu1]

It would be great if you could also mention the BigO for the solution. Thanks so much

[@Finn-jp6pn]

You're an amazing teacher .❤️ Please continue this series with frequent uploads.

[@samwilgost1143]

Please Please more of these interview questions, I love the way you explain them!!!

[@hemsagarpatel8992]

sir please make videos for various ds questions

[@VickieEB]

I just get excited when I see a notification from Java Brain. Thanks for this explanation. Clear

[@ajay-pg8ok]

Bro ur explanation makes everything easy to understand.

[@parvezmd6455]

Sir your way of explaining using pictorial diagram is super .

[@yuvaraj9740]

sir can you upload more questions asked on interviews in java please! thanks!

[@sisisisi6]

These interview questions are soo helpful. So helpful that I landed an offer from Amazon! Thank you!! So much.

[@ascar66]

How is it going in Amazon?

[@amirthasaha]

Thank you sir, can you please add a video explaining how Hashmap works in storing name value pairs and also the equals and hashcode method concepts around it. Thank you!

[@mukundpatel1768]

This is really nice sir.

[@saddamahmad2310]

thank you very much sir for this video

[@rashmir193]

Hi Koushik Cold you please add a tutorial to write a program that reverses a sentence. Ex: Hello World to World Hello

[@GenjaOrigins]

and how to check if they are palindrome foe example Anna and Reversed Anna is the same thing how to check this.. maybe with str1.equals(str2) something like this?

[@RANJANJHA95]

Expected to discuss most efficient approach

[@NANDANKAUSHIK]

How are you able to write like pen on paper , on whiteboard which seems to be running on your system ?

[@abarag8]

Hi Kaushik sir. Nice video. Keep up the good work. I am inspired from you and learned to love coding because of you :)

[@HungNguyen-nd6tz]

Thanks, it's perfect explanation

[@amitdeshpande2548]

When reference pointing to modified version of string literal then previous string would be collected by GC as it is not referred by any reference variable or it would remain in string pool without reference. In below code "Sachin" would be taken by GC or remains in string pool? class Testimmutablestring1{ public static void main(String args[]){ String s="Sachin"; s=s.concat(" Tendulkar"); System.out.println(s); } }

[@MetinCloup]

This is more practical package reverse; public class reversAString { public static void main(String[] args) { String a= "hello"; for (int i=a.length()-1; i >= 0; i--) { char c = a.charAt(i); System.out.print(c); } } }

[@pradiptalekar7545]

Hi Kaushik, really appreciate your work. Thank you!! Expecting more in this series - coding challenges

[@Paul-ry3jq]

These are really awesome, thanks for the good videos.

[@Tridib_Tinkel]

String str = "Hello World"; String f = ""; for(int i = 0; i < str.length(); i++) { f = str.charAt(i)+f; } System.out.printf("Reversed String: %s", f);

[@theblindprogrammer]

Good vid, keep up the good work.

[@aoshi2552]

Excellent video. Here’s my like 👍🏼

[@maheshgowthamt]

Hi sir, thanks for uploading videos for us....I need junit testing for controller and service classes in rest api using mockito..plz upload with explanation..

[@toufiqurrahman7025]

please continue this series

[@explorerfl007]

I think we can have solution using recursive method call. What are disadvantages of recursive calls?

[@Java.Brains]

Good point. Please refer to my pinned comment.

[@darylphuah]

Recursions are memory intensive in non-functional languages like Java. Not sure I agree with Java Brain's assertion that recursion is a cognitive load, if anything its normally simpler and easier to understand vs iteration. Tree traversals for example are better expressed recursively vs iterative.

[@balaramnayak9948]

Can we use character[] to hold the character and construct the String at the end?

[@theblindprogrammer]

String first = "First"; char[] chars = new char[first.length()]; for (int i =(first.length()-1); i>=0;i--){ chars[i] = first.charAt(i);; System.out.println("Character: " + chars[i]); }

[@ritesh_b]

Nice code sir👌

[@praveenj3112]

Such a easiest problem in interview

[@ariel-jc5ug]

Please make a Java course

[@DeepsWar]

Couldnt we also use stack and just print out the reversed string?

[@narimo2773]

Also possible option is: private static String reverseString(String str) { StringBuilder builder = new StringBuilder(); for (int i = str.length(); i > 0; i--) { builder.append(str.substring(i - 1, i)); } return builder.toString(); }

[@vignesh4352]

Hi Koushik, I am becoming a sincere student of your tutorials. Your logical explanation makes us to understand the concept clearly....I've been searching for DS and Algorithms tutorial for very long time. Even joined online tutorials on Geeks for Geeks, but its only waste of money. I know its very big concept to make ready, but at least give us planning how we can start learning it.

[@mahdighribi4151]

Thank you

[@SuperYouthful]

Int[] StringArray = String.toArray(numString); String revString = new String(""); For(int I = StringArray.length -1, I--, I >=0) { RevString += ("" + StringArray[i] ); } Return RevString;

[@malinmalindic8582]

Very nice way to find out , is a String a palindrome

[@sidharthk.burnwal2044]

keep making these kinds of videos brother :-)

[@davidparker5530]

Your manual solution is incorrect and it stems from a common misunderstanding of how strings are represented in Java. In Java, Strings are encoded using UTF-16, so you should preserve the relative ordering of UTF-16 surrogate pairs, i.e. this method fails to correctly reverse a string of code points outside of the basic multilingual plane, for example, emoji characters. In Java, the StringBuilder class already accounts for this if you use the reverse() method, so you should compare its output to your manual reverse on a string of emoji characters, or perhaps Egyptian hieroglyphs.

[@Vithal_Nivargi]

thank u sir

[@gs-rc3eq]

Thank you, Sir!!!!

[@dhanushkakumarage1889]

Thank you very much 😎

[@khadijabensaid2901]

Thanks a lot

[@vinitkatti7998]

public String reverse(String str){ if(str.length()==0){ return str; }else{ return reverse(str.substring(1)) + str.charAt(0); } }

[@MrRadebg]

String reverse(String s){ if(s.length() == 0) return ""; else { return reverse(s.substring(0)); } }

[@vegahimsa3057]

StringBuilder.reverse is about 10x faster than String += charAt(). StringBuilder is only a bit faster than StringBuffer on my computer. StringBuilder.reverse: (200 - 512 - 4041) ns StringBuffer.reverse: (230 - 566 - 4442) ns char[] reversing outer to inner: (422 - 1325 - 8646) ns String += charAt() for end to 0: (1277 - 5667 - 29 834) ns

[@ngonimugandani4504]

private static String reverseString(String s){ char [] n = new char[s.length()]; int counter = 0; for (int i = s.length()-1; i > -1 ; i--) { n[counter++]=s.toCharArray()[i]; } return new String(n); }

[@TomarSahab]

Swap char from 0 to length -1

[@manu-g21-mx]

Now with recursive :D

[@katiesun1533]

👍👍👍

[@kvelez]

My solution? package javaapplication21; import java.util.Scanner; public class JavaApplication21{ public static void main(String[] args) { Scanner scan = new Scanner(System.in); System.out.println("WORD: "); String word = scan.nextLine(); StringBuilder sb = new StringBuilder(); System.out.println(sb.append(word).reverse()); } }

[@danteastudillo6123]

return "oso" == new StringBuilder("oso").Reverse().toString()? true : false

[@aliali-uf9yp]

I would use recorgen🤔 much faster

[@asashish905]

As usual, I can die to watch your tutorials.. ❤️

[@vegahimsa3057]

Create a char[] .

[@chiranjeevisaride]

Lol which tech company asks String Reverse in coding interview then interviewer is dumb

[@onestepahead4507]

I think as Indian u should also speak hindi,

[@nareshbalabathula6062]

Can we use StringBuffer instead of StringBuilder ?

[@SushilKumarBhaskar]

Actually StringBuffer class having synchronized methods, that`s why it is slower than StringBuilder. you may use but think a case where size of string is about 10000+ char or more?

[@nareshbalabathula6062]

@@SushilKumarBhaskar got it.. Thanks

[@monkpintoo]

😔

[@Java.Brains]

Why the sad face?

[@monkpintoo]

@@Java.Brains I am waiting for array and stack video.

[@rohitmehta3812]

@@Java.Brains How to append using String???

[@explorerfl007]

@@rohitmehta3812 use '+' operator. result = result + str.charAt(i);

[@alemayehuaklilu7694]

@@monkpintoo a