Recursion Subset, Subsequence, String Questions

This is part 1 of the subset + string #recursion series. Here we cover some important tips to solve string recursion problems, along with subset patterns and how to convert recursive programs to iterative.
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=========================================
Timestamps:
0:00:00 Introduction
0:01:40 Basic String Questions using Recursion
0:02:19 Q1 : Skip a character
0:17:30 Q2 : Skip a string
0:21:32 Q3 : Skip a string if it's not the required string
0:24:34 Subsets Introduction
0:31:35 When to apply subset problem?
0:32:35 Q4 : Subsequences
0:43:11 Q5 : Return an ArrayList of string
0:52:10 Q6 : Print ASCII value of a character
0:54:15 Q7 : Subsequences with ASCII values
0:58:21 Q8 : Iterative program to print subsequences
1:09:48 Complexity Analysis
1:12:15 Q9 : Subsequences of a string with duplicate elements
1:22:07 Outro
#placement #dsa #interviews

[@aakashprasad9777]

Brother you are legend Several videos I have seen but I never understood these concepts You made these thing so easy Thanks Brother for such a beautiful and lovely content Concepts are fully cleared With the help of these videos now I have the faith and confidence to crack good companies Thanks Brother once again Great going Keep it up and deliver content like these

[@KunalKushwaha]

Thank You 🙏

[@gouravsyal2052]

@@KunalKushwaha at 1:16:50 we should not sort the array as it will rearrange the array and subsets will be wrong. And we know in subset : 2, 1, 2 is the subset of 2, 1, 2 but 1, 2, 2 is not subset of 2, 1, 2

[@GameDevNations910]

​@@gouravsyal2052 yep bro

[@GameDevNations910]

2,1,2 is subset of 2,1,2

[@GameDevNations910]

​​​@@KunalKushwaha sir it change order of array 2,1,2 while sort it become 1,2,2 1,2,2 is not subset of (2,1,2 ) .(2,1,2) is subset of 2,1,2 1:16:08

[@amruthaa5876]

If someone had skills like you especially the way you teach, they would launch this course as a paid one. Let it be anyone in this world. But you're here trying to help students like me and I'm very grateful. Thanks a ton, Kunal!

[@dickharry910]

Dont give him ideas!

[@poojabennabhaktula4883]

I dreaded recursion subset problem for almost an year now, and I stopped practicing because I was not very good with recursion. Now I can re-begin and work my way to FAANG

[@jamtaranumber2841]

me in the situation where i cant understand subset problems specially when for loop is used

[@sameerakhatoon9508]

@@jamtaranumber2841 you still struggling w/ iterative approach? lemme know, i can help you, can share the explanation here

[@jamtaranumber2841]

@@sameerakhatoon9508 yeah can you share your discord / linkedin

[@dubeyarts8661]

Sister are u in good company now?

[@shanmukhasivasai8335]

First I found Difficulty in understanding the subset problem . After carefully going through I too got it .This guy is awesome

[@sadmansakibmugdho4134]

Hello Kunal. I want to know, After the DSA course, will you show us how to use our skills in open source and all that stuffs till how to approach in a company? If not then please consider this.🙏🙏🙏

[@arunny9430]

No one taught me recursion like you. I, like many others like me, initially thought I understood recursion completely after watching the Fibonacci and Factorial examples. But then the reality hit when I tried to solve some medium-level problems. I realized that my concepts are so hazy that I had no clue how to apply anything I learnt in logically writing code to solve a problem. This site not only taught me the concept, but it is also so thorough that it forced me see what is happening from different angles and write code in multiple ways. Thanks, Kunal, for making recursion as clear as algebra instead of it being some monster like vector calculus or something. You are so thorough. Awesome.

[@Cloud-577]

no one explained recursion in so much detail like Kunal. Please someone give Kunal a medal already

[@anujar5508]

This is such a great video and it's incredible that you are not charging for sharing this immense knowledge. Just love the way you first explain the approach ,how to think and then actually solve the problem.Thankyou so much for these videos . And please please upload the graph and trees series 🙌

[@singhsuryanshu]

Kunal, I cannot believe this is so easy. I wrapped my head around with backtracking a lot and was still confused. Even took sessions of a paid educational website to understand backtracking. And literally I just watched your video once and all concepts are clear. You are legend.

[@manavarora7644]

+1

[@rishika9102]

Hii can u please tell me that is this course worth following as m a beginner no programming background plz reply confused

[@rishika9102]

@@manavarora7644 Hii can u please tell me that is this course worth following as m a beginner no programming background plz reply m confused

[@Gookun]

@@rishika9102 PICK A programming language first, then learn it.

[@chaitanyaprasad6924]

Amazing!!!! You proved that a good teacher is not one who tells all the solutions but someone we can lead us to all solutions. As once I listen to you logic coding has become damn easy!!

[@shakibsiddiqui2999]

Bro when i see your video it gives me confidence 👍

[@armaanthakur8116]

Everytime you make me like your video no matter what I don't know anyone who explains every small things like you I love that you made this beautiful course for free even though it's so much worth. May krishna bless you !

[@simranpreetkaur114]

In ques 9 we can just check if outer list contains that subset. If it doesn't contain, then only we should add it in outer. This way we'll avoid duplicates: public static List subsetDuplicates(int[] arr) { List outer = new ArrayList(); outer.add(new ArrayList()); for(int num: arr) { int n= outer.size(); for (int i = 0; i < n; i++) { List inner=new ArrayList(outer.get(i)); inner.add(num); if(!outer.contains(inner)) outer.add(inner); } } return outer; }

[@akashdeepgupta2085]

1:21:31 it will be good if we sort the array first, for the test cases like [1, 2,2,2] or [4, 4,4,1,4]. otherwise it will fail.

[@its_shivam_jha]

Great job man!

[@kcalbduorp3499]

.contains will take another internal nested loop so it increases the time complexity...

[@akashdeepgupta2085]

@@kcalbduorp3499 yes

[@omkarg01]

24:52 - 24:58 If I am not wrong, sliding window has not covered.

[@rakeshpotnuru]

Don't worry he keeps track of syllabus on github issue, maybe mistakenly said that.

[@jamespeterson7824]

'Recursion made easy' by kunal. Good Intuation, Thought process and superb way of teaching. Good work 🙂

[@Helly_Patel]

Thanks for teaching us like no one did till now!! One small request, please make lectures on dynamic programming as well!!

[@jatinkoli3389]

just started ur dsa course and fell in love with that

[@misbashaikh3357]

This video took me 8 hr to get completed but it all worth it. Thank you so much ❤

[@aakashyadav9117]

you are genius man , i did the subset problem of string "abc" and i used loop inside that , and you simple printed using recursion 🙌

[@user-mk8zz3ow4f]

Incredible course, the concept which you tell us in the starting of the recursion is enough to solve this problem and the track the answer in the function body is the awesome way to hold the answer more then the in the arguments

[@hindutva5646]

After all that your efforts and following all the previous playlist videos , Now i get some confidence in DSA to solve problems easily . Thanks Kunal bhaiyaa (Sir) for all that quality Content that i hunt for all over youtube

[@bhavyabansal1143]

Thank you so much for explaining this beautifully. When can we expected videos for DP, graphs and trees?

[@beb57swatimohapatra21]

Finally!!! I understood these topics... you r a legend kunall

[@prasadm3614]

Insanely simple explanation of subsets... M awestruck

[@dickharry910]

Another great video. Thanks for the good work Kunal. Wish you the very best!

[@whatwelearntoday]

This is the first time that i understood recursion in subsets after a lot of hunt for this material .Thanks a lot!

[@KunalKushwaha]

Glad to hear that!

[@rakeshsagar9510]

I find his sub sequence tutorials much informative and communication is superb.

[@mohammedadnan2449]

Q9 : Subsequences of a string with duplicate elements Can be solved in easier way with the code snippet mentioned below:- ------------------------------------------------------ List outerList = new ArrayList();//outerList outerList.add(new ArrayList()); for (int num : arr) { int size = outerList.size(); for (int i = 0; i < size; i++) { List internalList = new ArrayList(outerList.get(i)); internalList.add(num); if (!outerList.contains(internalList)) { outerList.add(internalList); } } } return outerList; ---------------------------------------------------------

[@user-py4et2qk3c]

contains method takes O(n) of time then it leads to O(n^3) for overall time complexity

[@user-py4et2qk3c]

static List subSetDuplicates(int[] nums) { Arrays.sort(nums); List outerList = new ArrayList(); outerList.add(new ArrayList()); for (int i = 0 ;i < nums.length ; i++) { int start = 0; int end = outerList.size(); if( i > 0 && nums[i] == nums[i - 1]){ start = start + (end - start ) / 2; } for (int j = start; j < end; j++) { ArrayList intenalList = new ArrayList(outerList.get(j)); intenalList.add(nums[i]); outerList.add(intenalList); } } return outerList; }

[@varunkumar6223]

for the last question instead of adding the start or end index , if found duplicate just start the inner loop with outerarray size / 2 and it works fine #include using namespace std; vector subsetrec(string main,string pro){ vector s; if(main.empty()){ s.push_back(pro); return s; } char ch = main[0]; vector s1 = subsetrec(main.substr(1),pro); vector s2 = subsetrec(main.substr(1),pro+ch); s.insert(s.end(),s1.begin(),s1.end()); s.insert(s.end(),s2.begin(),s2.end()); return s; } void subsetitr(){ vector v{1,2,3,3}; vector res; res.push_back({ }); for(int i=0;i 0 && v[i] == v[i-1]) j= (n/2); // LOOK HERE for(;j

[@gnanaprakashm843]

Can you explain your thought process behind why it works ?

[@laxminarayanakoyyana1753]

@@gnanaprakashm843 he is just removing duplicates bro , that's it.

[@gnanaprakashm843]

@@laxminarayanakoyyana1753 I see I'll look into it. thanks 🙏

[@charon71]

it is unbelievable how easy you can solve recursion tasks after watching these videos. You really get told HOW to think. Thanks alot!

[@KunalKushwaha]

So nice of you

[@mohamedjasimazizg442]

I have been watching your videos for so long it's been very helpful to grow personally

[@aniketshetty6694]

Your confidence level is what makes you different from others. The best dsa course ever!

[@rockrk2519]

can anybody please tell in which video kunal has covered sliding window...

[@poorpanda9033]

@@rockrk2519 he hasn't covered yet he definitely will

[@sriharshakandurivenkatases2587]

We are grateful to you for the knowledge you are providing for free🙏🙏 Waiting for your next DSA video #DSAWithKunal❤

[@mathlover7688]

ye kya ho raha dsa se main bore kyon nhi ho raha ye toh magic ho gya kunal bhai ,love you bhai aisa best content ke liye ab lag raha main sikh jaunga dsa

[@abdulrauf7815]

The definition and recursion tree for subsets was very very great❤❤

[@arishkhan6300]

Brother you are legend i see the spirit in you to become s Minecraft stremer . You will achive great success as gamer.

[@anuragbudakoti755]

Dhanyawad apka iss DSA course ke liye

[@dsrfacts6483]

Amazing content bro... Keep doing the good work..Lots of luck 🎉

[@gauravdham9982]

Great work bro !! Keep it up and keep making such videos for others to learn!!

[@DSrikanthd]

This is just brilliant Brother, Keep doing it. Just waiting for the DP series, Please do it soon.

[@vaibhavghatge8553]

Really awesome way of teaching finally, thinking in the recursive way, |2^n sub set

[@prempeacefulchannel]

Legendary way of teaching! Thanks brother

[@KunalKushwaha]

My pleasure!

[@faizanhaider3953]

phele to dur se pair chu k parNaam bro 🙏🙏 DhanSuuu lecture Kunal bhai... Nobody teaches like you.. but plz complete krdo bhai playlist... 🙏🙏

[@alonbrim]

Great Video! Very well explained! Great job Kunal, thank you very much!

[@KunalKushwaha]

You’re welcome

[@projectsdb4034]

Thanks for the great tutorial please continue the series

[@adityapalve3752]

very good video, i used to detest recursion kinda like it more than iteration now

[@kishanpareek2848]

Ye Kunal ka course bhot mast hai. Sab samaj aa gya

[@rishabhrawat8197]

touched my heart as always

[@panchanansahoo1463]

Nice video kunal. For the last question we can add a check before adding the inner list to the outer list, If the outer list already contains the inner list or not

[@subhankarkanrar9494]

Just Enjoying every moment ❤. Love it😊

[@davidmwangi4312]

Best recursion series I have watched.Excellent explanation. Thanks Kunal

[@KunalKushwaha]

You are most welcome

[@ombhandari6148]

Thank you brother Finally I understood how to solve the subsets problem.. Thanks a lot brother. You are doing great

[@KunalKushwaha]

More to come

[@apurwarokade3863]

You are a genius kunal 😊

[@yashkoolwal196]

One of most awaited vidoe

[@aakashgoswami2356]

Other : How to solve a problem. Le kunal : How to approach a problem.

[@KunalKushwaha]

That was the plan

[@vanshsharma2486]

great video bro, thank you so much!!

[@andretheruler714]

recursion is still hard but you explained it well

[@techmechanical399]

U r simply genius bro

[@ragulp5489]

Thanks bro all the concepts u deliver is so clear sir. pls make some vdos on windows sliding, two pointer approach too sir.

[@aasisinha6100]

Truely informative and lots of creativity in teaching...became friend without meeting you..

[@BrajBliss]

This and the merge sort video are the only one I just can't get in my head.

[@nagasatya5969]

Kunal, please try completing the series. It'd be of great help. cuz of all the videos I've watched on recursion, all of them were very specific to the prlms they taught and none of them explained how recursion actually works. I don't think they'd do any better with topics like dp. So, if you can, complete the series

[@govindvarshney5116]

bro that was ammazing.

[@siyavats6892]

thank you so much kunal♥

[@user-ue2wo1uk7x]

Please make a video on subarray concepts

[@gitanshutalwar1604]

Bro this content is great. thanks for your effort Just one question man how did you get this much knowledge

[@koushanikarmakar5159]

Thank you so much ! I always had problems with these type of questions. I have better grasp on these topics now.

[@sameerakhatoon9508]

for qn 9, please find my recursive solution below approach: if we ignore the occuring of duplicates char means we ignore each of that duplicate char public class Recursion{ public static void main(String[] args) { System.out.println(subSetsWithDupInString("122", "")); } static ArrayList subSetsWithDupInString(String str, String ans){ if(str.isEmpty()){ ArrayList ls = new ArrayList(); ls.add(ans); return ls; } char ch = str.charAt(0); ArrayList left = new ArrayList(); ArrayList right = new ArrayList(); int i = 1; while(i

[@karthick7983]

10:05 le kunal : ccd le siri : yeah bruhh!! LOL.

[@devesh819]

A new episode of recussion session 😂😂

[@siddhigupta7673]

pls kunal complete the course no other course can match the level of content u were providing

[@akashnag6459]

Easiest explanation of recursion in internet.

[@payalsamanta3139]

please continue the series

[@missyanshi9279]

thankyou for this course ...please upload more videossssss😭😭

[@govindvarshney5116]

you killed it bro

[@alpersener4269]

bro you're awesome thanks for the concepts you have taught us.👑👑👑

[@SAIFALI-rn5cs]

Bro, why I am getting error at p:p+ch, saying as Syntax error on token " : ", invalid AssignmentOperator.

[@akashpal3947]

@Kunal Kushwaha In place of using s and e in the Q9 for the starting of the loop..can't we just start it with N/2 of the outer.size() if its duplicate ?

[@ritikadhiman101]

He is really good!

[@atharvparlikar8765]

Waa ye hi time mila tha upload karne ko 😐

[@wenli724]

You are the best !!! please make some video about DP thanks ahead!!!

[@PrasunKundu]

Wait kar rha tha iske liye....

[@nevermore7755]

Hi Kunal, thank you so much for the content! Do you know where I can find Dynamic Programming playlist? I couldn't find it anywhere on your channel. Thanks again brother

[@samworld7923]

I thought to take half of outer list size as start index, but sooner realize what if multiple duplicate elements are coming, it will fail to survive that condition

[@anuragsingh4400]

please schedule one orientation meeting for maitians ❤️ I'm also from mait cse you are idol for lots of us 🙏🙏🙏

[@plutomessi21]

In this example, the recursiveSubstring method prints the current substring and then makes a recursive call with s.substring(1). Each recursive call creates a new substring starting from the second character of the previous substring. Output: vbnet Copy code Substring: abcdef Substring: bcdef Substring: cdef Substring: def Substring: ef Substring: f Empty String

[@ketara1234od]

you are the BEST !!

[@suhaibalam1040]

Brother can you please tell me which keyboard you are using

[@harshjaiswal1634]

Recursion session... Just like therapy session

[@RakeshkumarD-py9iz]

hey kunal..still u didn't upload dynamic programming, graph, trees etc.....

[@suzanaangboo2448]

difficult to understand iterative and duplicate problems :(

[@joeabala2037]

Excellent!

[@kushalava007]

Shall i use C++ list with splice() to imitate java's arraylist used with addAll()?

[@sourabhsahu961]

Bhaiii you are legend, when you are coming with OOP java tutorials

[@mrrishiraj88]

Thanks a lot

[@navnav1819]

When I watch these videos I find myself saying to myself "very simple stuff" just like you haha

[@letstry.coding_2816]

Thank you so much

[@ArunSharma-wg9xw]

Can you share the link of the podcast mic 🎙️ which you use in your videos?

[@Yashasvee2003]

since a set does not allow duplicates , so shldnt (2,2) , (1,2,2) be removed from final answer ?

[@jatinkoli3389]

Bhaiya i am getting admsion into DTU CS can u please make a video 1st year roadmap I was waiting to get into college to start programming with ur course Loving ur confidence and content

[@devjoshi7062]

kzbin.info/aero/PLPX75d4curILdTmhcM5iJ6ReNx-LKW12P here, these are old videos of kunal when he used to work with a ed-tech, he has made a complete 4 year roadmap for B.Tech students

[@dakubhai6014]

U r diamond dude...May lord protect u from Aliens for the boon of mankind.