L6. Recursion on Subsequences | Printing Subsequences

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[@jaimitkumarpanchal7603]

Man i usually don't comment on KZbin videos, but i just solved 3 medium level questions in under 20 mins. Damnnnnnnn i have no words to express. but this video specifically is a gem to solve most of the recursion sub-seq problem. Thank you so much 😄 Edit : i have watched this video 2-3 months back(December) for dynamic programming, till this day i remember every detail of the video.

[@mrsmurf911]

from sklearn.pipeline import Pipeline import sklearn.svm from sklearn.linear_model import LogisticRegression knn=KNeighborsClassifier(n_neighbors=8) rfc=RandomForestClassifier(max_features=2,n_estimators=64,bootstrap=False,oob_score=False) svm = svm.SVC(kernel='rbf',C=1,gamma=1) lr=LogisticRegression(C=0.01,max_iter=100,penalty='l2') # define the pipeline # define the pipeline pipe = Pipeline([ ('scaler', StandardScaler()), ('knn', knn), ('rfc', rfc), ('svm', svm), ('lr', lr), ('preds', FunctionTransformer(lambda x: x.predict_proba(x)[:,1].reshape(-1,1))) ]) # fit the pipeline to your data pipe.fit(X_train, y_train) # predict on new data y_pred = pipe.predict(X_test) # evaluate the pipeline's performance accuracy = pipe.score(X_test, y_test)

[@stain5570]

hii, may I know what are you doing right now

[@samratpatel8060]

@@stain5570 he is a SDE-3 at CornHub

[@SUJAYNIRANJANNAIKCSE23D]

​​@@stain5570 same question ⁉️

[@ashwanisharma8903]

Best thing is you have very deep understanding of the topics and you code your own way. While other videos mostly pick code from GFG and explain which goes above head. Thanks for lovely explanation.

[@jaibhagat7441]

Huh

[@aeroabrar_31]

The code for printing string subsequences. package Recursion_2; import java.util.ArrayList; public class Subsequences { public static void main(String[] args) { String s="abcd"; char[] c=s.toCharArray(); print_string_subseq(new ArrayList(),0,c,s.length()); } public static void print_string_subseq(ArrayList al,int ind,char[] c,int n) { if(ind>=n) { if(al.size()==0) System.out.print("{}"); for(char t:al) { System.out.print(t); } System.out.println(); return; } print_string_subseq(al,ind+1,c,n); al.add(c[ind]); print_string_subseq(al,ind+1,c,n); al.remove(al.size()-1); } } Output : {} d c cd b bd bc bcd a ad ac acd ab abd abc abcd

[@roshangeorge97]

He is unique XD

[@sanjayhazra181]

Yup, also some just mug up from chatgpt and code .

[@AbhinavKumar-tg4il]

after watching 3 times, now understood. Those who are not able to understand, it's okay, retry, you will get it, and after that you will feel good.

[@dgvj]

Best series on recursion in the internet. Thanks alot for your time and effort.

[@tharundharmaraj9045]

Simple english....No confusions......... Great work

[@sarathchandra941]

Finally, the day has come to understand and as well code for the same.

[@ashutoshthite]

💯💯

[@sniper_army3735]

Amazing man, doesn't even know us, isn't even related to us, but still is doing so much for the students aspiring to be software engineers. People like him are the ones who become inspiration to others to bring change to the society.

[@ujjwalshrivastava3594]

Bro I still not able to understand recursion very much confusing to me

[@xdjqye]

@@ujjwalshrivastava3594 try to draw the recursion tree alongside striver, it really cleared up things for me

[@jayeshbangar8373]

JAVA Code- public static void sub(ArrayList al, int arr[], int i){ if(i == arr.length){ System.out.println(al.toString()); return; } al.add(arr[i]); sub(al,arr,i+1); al.remove(al.size()-1); sub(al,arr,i+1); }

[@jatin_lanje]

with small correction public static void sub(ArrayList list, int arr[], int i){ if(i == arr.length){ if(list.size()>0){ System.out.println(list.toString()); } return; } list.add(arr[i]); sub(list,arr,i+1); list.remove(list.size()-1); sub(list,arr,i+1); }

[@mayankshukla7195]

thanku so much brother

[@travelnlearn]

THANK YOU BRO, BEST PART: YOU COmpletely connects with your audience and each and every step goes direclty into our brain and we understand everything. Thank You & keep it up

[@potatocoder5090]

Brilliant explanation! I never quite understood this question before watching this video. The take/not take pattern is going to be in my head forever. Thank you so much! You're an amazing teacher :)

[@ShubhamSinghMr.s]

JAVA CODE FOR THE SAME WILL BE ::- public static void main(String[] args) { int[] arr = { 3, 1, 2 }; ArrayList list = new ArrayList(); printSub(0, arr, list); } private static void printSub(int i, int[] arr, ArrayList list) { if (i == arr.length) { System.out.println(list.toString()); return; } list.add(arr[i]); printSub(i + 1, arr, list); list.remove(list.size() - 1); printSub(i + 1, arr, list); }

[@badboybb519]

It helped me a lot bro

[@klakshmisuryateja8320]

Very helpful

[@pehdntene6473]

I do not understand one thing if we try to apply the same logic but when the return type is List this doesn't work cause instead we get an empty list when i == arr.length

[@VollalaPavanSathwik]

@@pehdntene6473 import java.util.ArrayList; import java.util.List; public class rec_subseq { public static void main(String[] args) { int[] arr={3,1,2}; ArrayList list = new ArrayList(); ArrayList li= new ArrayList(); subseq(0,arr,list,li); System.out.println(li); //System.out.println(li.toString()); } static ArrayList subseq(int i,int[] arr, ArrayList list,ArrayList li) { if(i>=arr.length) { li.add(list); return li; } list.add(arr[i]); subseq(i+1,arr,new ArrayList(list),li); list.remove(list.size()-1); subseq(i+1,arr,new ArrayList(list),li); return li; } } Try this

[@phaneendra_guduru]

Thank you brother 😊

[@NiyatiShah24]

You made it much simple to understand! A true teacher! Thank you 💚

[@yotowilliam5465]

Amazed by your lessons, i feel like i know recursion better than before, thanks bro.

[@adityadeshbhartar7172]

What a explaition strting from base case to dry run to recursion tree , Fully fantastic, even i used to code in java still noone can reach your level of explanation ❤🤘 Best video...

[@ayushuniyal2586]

after watching many videos on recursion ,i was not able to do dry run of recursion question .Now i can say this is the best explaination for begineers to do dry run and understand recursion.just fantastic bhaiya like how easy you explained .hats off nailed it respect++.

[@ujjwalshrivastava3594]

How to learn recursion?

[@sureshgarine]

indeed, it's a wonderful explanation. thanks for taking time and doing this for community

[@ardhidattatreyavarma5337]

after this video I solved subset sum pretty easily. Thank for your crystal clear explanation

[@habeeblaimusa4466]

I had to watch this video for more than 5 times. God bless you bro

[@jyotirmoy_dey]

This guy makes recursion look easy and fun. Kudos to you! Amazing job, very inspiring!

[@soumyajeetsengupta3064]

I have seen soo many videos for this problem and never understood anything but your explanation it was awesome it gave me confidence to solve any problem of this kind(take or not take). Thankyou Striver sir!

[@ShubhamKumar-sj6dp]

or it could be opposite , since you tried it many times , this was the time it clicked , it would have been same if you would have watched this video first and other video would have clicked !!!!!!

[@udaykulkarni5639]

Man! This is crazzyyyy!! I never really comment on KZbin. But this is some next level shit ! I kept memorizing the subseq code as I was sure i would never understand this. But you have finally made it clear and I dont need to memorize it ! Its pretty straight forward! Thanks a ton😊❤

[@studynewthings1727]

Thankyou STRIVER, for explaining the subsequence problem in a awesome manner.

[@SumitTiwari-f7t]

Thankyou for making videos of recursion and covering all topics. It gives me confidence and boost-up in my rating.

[@samsmith3961]

this has been beautifully explained ..I've been searching for this explanation for hours now and this was good

[@AngadSingh97]

Excellent explanation, itni baar dekhne ke baad it is even possible to watch at 3x and revise easily, which is amazing.

[@visheshwaghmare7504]

If we want to avoid the remove part, we can first call without adding and then add the element and call function again with the added element in the vector.

[@amit2194]

if you want to remember it like using " take " and "not take " you should follow that

[@NitishKumar-yy9kn]

if we pass the vector by value, removal will not be needed

[@RishabhJain-iz5xk]

HANDS DOWN BEST EXPLANATION ON INTERNET!

[@iamabishekbaiju]

I watched it once didn't understand, but after that watched again by following him with a pen and paper and understood completely.

[@iitimunda]

02:18 Generate all subsequences for an array using recursion 04:36 Understanding the structure and pattern of code is crucial for solving problems. 06:50 Code implementation to create a subsequence using recursion. 09:16 By making recursive calls with different indices and choosing whether to include the last element, you can generate all possible subsequences of an array. 11:27 Remove elements from an array based on specific conditions. 13:39 Understanding the concept of adding and removing items in a sequence 15:42 Printing the values in a recursion tree 17:46 Printing subsequences using recursion 19:38 Print a data structure to display the subsequence 21:20 The algorithm involves picking or not picking elements from a given array. 23:10 Time complexity is 2^n and space complexity is O(n)

[@soorma7869]

Finally it's crystal clear... After watching this video 3-4 times

[@SuperWhatusername]

Earlier I was learning recursion and dynamic programming together and that was my mistake. Thanks for creating this playlist and awesome explanation.

[@azaanakhtar1974]

Uh are write in which language Cpp Or java

[@azaanakhtar1974]

I wrote in java bt i faced an error working with array and list

[@SuperWhatusername]

@@azaanakhtar1974 CPP

[@ratanmasanta3210]

@@azaanakhtar1974 Try this: static void findSubsequence(int index, int[] array, ArrayList arrayList) { if(index == array.length) { System.out.println(Arrays.toString(arrayList.toArray())); return; } arrayList.add(array[index]); findSubsequence(index+1, array, arrayList); arrayList.remove(arrayList.size() - 1); //need to remove last element findSubsequence(index+1, array, arrayList); }

[@azaanakhtar1974]

@@ratanmasanta3210 thanks buddy

[@aravinda1595]

Thanks a lot sir,I have been frustrated since a long time because of recursion ,it felt impossible for me to solve any leetcode problem but after your series i feel more confident in approaching any backtracking problem.You just don't explain a solution for a particular problem but a solution which can be modified and used for any other similar problem.

[@ujjwalshrivastava3594]

Bro how u understand recursion?

[@abdullahaladibakhand960]

We can do it without even deleting. We can follow the following procedure : at first call recursion function for not pick then add the element to it and then call recursion function with picking the current element. It will also cover all subsequence. But we do not need to delete the unpicked element.

[@akshaybhagwat6179]

The best explanation ever exist on the youtube.

[@rumiNITPatna]

thank u so much striver ! i was struggling with this one and i finally understood this using recursion tree.. THANK YOUUUUUUU

[@sojwalgosavi4406]

You are taking great efforts and we are learning from you Striver.

[@AkshatMehra-l4b]

Amazing, lost for words 👏🏽👏🏽👏🏽

[@ashokdurunde1814]

Thank you so much! You're an amazing teacher :)

[@Codebond7]

Understood. will complete recursion today no matter how much time it takes.

[@arnabkundu1648]

I have understood it extremely well. Thank you sir.

[@wassupCraji]

This was some crazy cool thing to learn today had so much fun!

[@Cool96267]

Hey Striver, Could you also please attach the link of the respective leetcode questions?

[@godessGOAT]

found?

[@Dheeraj-ed6rr]

@@godessGOAT Leetcode 78

[@akshanshsharma6025]

@@Dheeraj-ed6rr thanku bro

[@vinnuhary2198]

mad respect to this man for keeping it super simple

[@madhujustin2124]

STARTED YESTERDAY, IT CAN BE HELPFUL FOR THOSE WHO STARTED NOW...LIKE ME... PYTHON CODE FOR THE SAME IS: def subseq(index, current,arr): if index >= len(arr): print(current) return current.append(arr[index]) subseq(index+1, current,arr) current.pop() subseq(index+1, current,arr) arr = [3,1,2] index=0 subseq(index, [ ] ,arr)

[@sid1993ful]

What if we are not to print but instead create a list of list and return that?

[@vvssreddy903]

I have a small doubt, during 3rd recursive call the list is [3,2,1] and i value is 3. Now as i= arr.length, we print the list. After that to back track, we remove recently added element which is 2. Now the list becomes [3,1] but the i value doesnt change. It remains same 3.and after removing, we did sub(al,arr,i+1) which is sub([3,1],arr,4).im confusing here

[@arshadshaik4961]

When we reach I=3 we actually increase for the branch which is going through right side for left side branch also we get I=3 only because we had called the both right side and left side branches in same function which is f(2, {3, 1}). Just go with tree and you can easily understand

[@gwalaniarun]

Awesome man, love your explainatiton.

[@tarun1684]

Apart lecture..vdo end m jo gaane ki tune chlti h.. like it..😂😂❤

[@sreenandini766]

Super explanation sir .Thank you so much❤️

[@sumitvishwkarma6907]

Now I understand this subsequence, after watching famous courses of CN, CB, I don't understand from them that deeply

[@Ayushkumar-co9mc]

Thanks a lot sir, now its crystal clear i made 2-3 recursion trees by my own it took me an hour but now its very clear.

[@sagarsinha6561]

Hey Striver, your approach is superb. However, I have followed another strategy which is more intuitive for me, the code for which is: def fn(i, n, arr, osf): if (i >= n): print(osf) return fn(i+1, n, arr, osf) fn(i+1, n, arr, osf+str(arr[i]))

[@sagarsinha6561]

In your way, it can be termed as don't pick-pick strategy (yours being pick/remove) 😅

[@ramyavennapusa736]

But, somehow for printing the subsequences of an array, this method is failing

[@sharmakartikeya]

Just don't stop uploading anytime you feel you are not getting enough views. Good Luck.

[@sumanthvarmakarampudi7251]

Super Clear, Great Effort Always thankful to you sir

[@Malayalam_learner]

ధన్యవాదాలు ❤

[@chandan1929]

if I don't pass the vector &ds as reference then I don't have the need to ds.pop_back() correct ??

[@takeUforward]

Then it creates a new copy everytime, which will lead to tle :(

[@ryanmathew6397]

That really was one of the best way to explain sub-sequence.

[@kanishkasingh2324]

Humour and wit with abundance of knowledge and talent!

[@horccruxxxop4184]

Hello bhai. 12:07 pr when we had popped 2 then it can to next line where ind+1 should be done but you had passed 3 why??

[@niitteenpathak5620]

Thank you so much for amazing explanation.

[@omkarwarule5483]

one of the beautiful play list for recursion on you tube

[@factsmotivation7728]

Thanks you so much sir for this wonderful content ,i loved with recursion sir 🙏🙏

[@sadmanmehedisivan6581]

It will be so cool if you can add the codes in the description!

[@shreeshah8745]

Can someone please explain why at 15:42, when we move to 'not pick' any value from array we still increase our index value to 1?

[@takeUforward]

Coz if u don’t pick, why will u stay on same index.

[@shreeshah8745]

@@takeUforward Thank you sir for replying. I got it now. 👍

[@saahilsharma6537]

Java Code :- public static void func(int i,List a,List arr) { if(i>=arr.size()) { System.out.println(a); return; } a.add(arr.get(i)); func(i+1,a,arr); a.remove(arr.get(i)); func(i+1,a,arr); } }

[@saira18926]

thank you

[@k10n28]

i was looking for the same thanks

[@hrithikrudra4292]

Bro,thnaks for this..But I am facing some problem while taking the input as array.. Error:For 2 it is showing out of bound index..Anyone help me out in this,issue??Thanks in advance My code: /** * PrintAllSubsequence */ import java.util.*; public class PrintAllSubsequence { static void printSubsequence(int index,ArrayList res,int arr[]){ if(index==arr.length) { System.out.println(res); return; } //taking the arr input res.add(arr[index]); printSubsequence(index+1, res, arr); //not taking the array input res.remove(arr[index]); printSubsequence(index+1, res, arr); } public static void main(String[] args) { int []arr={3,1,2}; ArrayList res=new ArrayList(); printSubsequence(0, res , arr); } }

[@swapnilnandedkar3930]

@@hrithikrudra4292 change your res.remove(arr[index]); statement with res.remove(new Integer(arr[index])); arrayList have 2 remove method one with index and other with object. res.remove(arr[index]); this statement try to call remove with index because arr[index] giving int and Collection only work with objects. Because of this you are getting outofbound. Either use new Integer(arr[index]) or convert int []arr={3,1,2} to arraylist

[@hrithikrudra4292]

@@swapnilnandedkar3930 thanks,bro..👌👌

[@bazeer1498]

after watching 5 times with paralally coding ..now i finally understand the whole concept of take and not take lol😆

[@MindMunchies.]

Thanks striver After watching it from all the tutors on youtube Finally i conclude you are a true gem 🤍 bro... will definitely meet you one day insha allah

[@alifaisal1475]

YOU ARE AWESOME! Explained this difficult topic with ease, and in-depth as well. ❤‍🔥

[@veekshithcb]

You have to keep it in your head everyday till your . retirement......

[@pratyushvaibhav]

Watched the intermediate few minutes thrice and finally understood , lesson I learn't : sometime we need a small self-upgradation to understand the educator , not always the teacher(educator) is bad .

[@green_lucozade]

in the code where not pick is before pick, why do we do pop_back after the function call for pick?

[@ironman-bz7wx]

9:30 , uare not passing the array in the method,how can we add arr[index] ?

[@Tbm4545]

Thats was just a dry run not actual code, just understand the process finally he has given the code too.

[@thisisrajneel]

why does the vector have to be passed by reference? at 20:07

[@sriramrajkumar2774]

Anyone clear me this doubt. At 22.38 striver changed not pick first then picked second i thing the pop_back is not necessary. Am i correct?

[@straightfacts5683]

i have same doubt couldnt understand that

[@consistency_Is_key]

watched it 4 times to understand this above 80% ,nice

[@Nitin-x4v]

at 8:05 i cant understand if an empty array is passed then hown can we say that the size inside the function will be 3?? can anyone tell me this?

[@manishchandrapaneru.o5]

The most beautiful explanation ✅

[@laginenisailendra1959]

May God bless you with all the health and wealth you need. I understood it.

[@parthsalat]

Thanks a lot for this priceless video!

[@Yash-uk8ib]

Sir, i can understand that i==n will be a base case but i>n will not happen.. as soon as i reaches n, it will return. I>=n is not making any sense to me. Correct me if I am wrong!!

[@yashverma2986]

Ha shi h tu bhi i==n hi shi h

[@shauryatuli2241]

I had the same doubt but I think the idea is i>= n (already contains i == n ) , the greater than sign is for extra precaution I guess or maybe because Bhaiya from the starting is teaching i>= n , in all his previous video ... maybe he want to show continuity in his code and teaching style

[@Yash-uk8ib]

@@shauryatuli2241 ok

[@nahidfaraji5069]

No one can beat this Explanation.

[@Highlights_Point]

Great Explanation sir i feel the recursion today

[@aashapun6533]

Thank you so much. Worthy Content!!

[@anshvashisht8519]

thank you so much for the recursive tree it helped a lot

[@iamnottech8918]

striver saved me he said remember it till the...... so when i was at gate of heaven they denied entry as i forgot it there so i got more time on earth to recap it , guys rules are very strict there. BE PREPARED 🤪

[@_sf_editz1870]

java code : if (index >= n) { System.out.println(list); return; } // Include the current element in the subset list.add(arr[index]); printSub(arr, list, n, index + 1); // Exclude the current element from the subset list.remove(list.size() - 1); // Remove the last element (backtrack) printSub(arr, list, n, index + 1); }

[@anishmishra4988]

I have a little curious question that why to remove them later why not first make the recursive call without taking the element and then later add it then made the recursive call ? If Order is not Important of the sub-sequences.

[@arohikarhade1954]

First of all, AMAZING and very helpful video. Thank you for all your effort. P.S. am I the only one who notices that he uses 'a couple of options' to tell us we have specifically 2 options. Not hating at all but I just got so confused at first haha.

[@joeyaintwaffling]

Aur tarakki mile aapko bhai, kya samjhate ho

[@sujalsamai6459]

So useful video. Thanks 👍🙏

[@mr.rexalan5576]

I can understand the code, but i can't able to think recursively on my own to code. Is there any solution for this

[@santhoshswamyv5627]

try to draw the recursive tree like him to get flow with the recursion

[@brp3522]

Try and fail then google is the only way I was in your position but today I conquered the recursion wholly. All the best bud

[@ritvi5717]

amazing teacher thank you so much :)

[@harshilsutariya1793]

striver content 💥 >>>

[@torishi82]

Bhai tum mahan ho. Samaj aa gaya.

[@md.sahidulislam3152]

You are the best....Love from Bangladesh

[@PawanSingh-ck2jv]

this code is giving output as 198 but bool value should only return 0 or 1. also i know that i can get correct output by using & variable as &s. #include using namespace std; bool palindraom(int i,int j,string s){ if(i>j)return 1; if(s[i]!=s[j])return 0; palindraom(i+1,j-1,s); } int main(){ string s="non"; bool k=palindraom(0,2,s); cout

[@purushottamkumar3140]

Hats'Off to this Guy. Amazing

[@muntajir646]

THE BEST ON THE INTERNET

[@debadityaghosh7612]

Best explanation on internet ❤

[@puranjanprithu6337]

the tree simplified everything...thanks man

[@47BOT]

When i try to understand using dry run of recursive tree method then i understand it very well . But if i try to do dry step by step then i get confused...