How To Reverse A Singly Linked List | The Ultimate Explanation (Iteratively & Recursively)

[@BackToBackSWE]

Table of Contents: (This was one of the first videos I made. Audio sucks. Lighting sucks. It is pretty bad. I'm sorry.) Intro & Video Setup 0:00 - 0:33 Problem Introduction 0:33 - 2:00 Iterative 2:00 - 6:08 Recursive 6:08 - 9:42 Recursive (Detailed Walkthrough) 9:42 - 13:26 Conclusion 13:26 - 13:49 For the recursive way forgot to stress the line saying "head.next = null", this ensures that you point the last node in the reversed portion (built slowly as we go upwards in the recursion) to null. This is important.

[@mrknight411]

As for the recursive solution, I believe people are confused about head.next.next=head and head.next=null operations because they're not seeing that both rlh and head are referencing the same mutable node objects in heap. In stack where head.data is 3: rlh is 4 head is 3->4 head.next.next=head is 3->4->3->4... head.next=null is 4->3, since it removes all "next" obj ref in 3 to 4, leaving intact 4->3 Since 4 now points to 3 in memory, rlh becomes 4->3 ** debug the recursive solution in your IDE and place a breakpoint on line head.next=null. You will see that rlh.next is now node 3. In stack where head.data is 2: rlh is 4->3 head is 2->3 head.next.next=head, which is 2->3->2->3... head.next=null is 3->2 2 Now rlh is 4->3->2 2 And now the main stack: rlh is 4->3->2 head is 1->2 head.next.next=head is 1->2->1->2... head.next=null is 2->1 , since the obj ref from 1 to 2 is removed Now rlh is 4->3->2->1 , since 2 now points to 1. Recursion is not easy to wrap your head around, especially when dealing with references (or pointers). You did a good job explaining the stack, but you missed the heap :)

[@sarfarazalam6077]

Yeah, I was also wondering why use "head.next = null". Thank you, for clarifying this! Thanks for the video!

[@BackToBackSWE]

yo

[@irfaanjamarussadiq5500]

Honestly I didn't really mind audio/lighting quality. But I think you could speak a little slower, because it kind of stresses me out when you speak so fast and it's also harder to understand that way. Beyond that, this was a really nice explanation!

[@BackToBackSWE]

@@irfaanjamarussadiq5500 old video

[@5astelija75]

I never imagined learning code would be this intense

[@WildThoughtsAI]

lmao

[@joshuamarcano350]

🤣

[@Working800]

I like your comment, it is a bitter true a few people discuss lol

[@anitasingh-jf1ql]

This is literally the best explanation of reversing a linked list on youtube!!!

[@BackToBackSWE]

thx

[@stinkykyle96]

You seem so excited to explain the problems, it makes your videos engaging 😁 But honestly this is some of the best interview prep that I've gotten, especially since I'm a visual learner.

[@BackToBackSWE]

Great! :) -Ben

[@fardin_shaik]

No one can explain recursive thinking better than you, man. Respect

[@BackToBackSWE]

hahaha thanks

[@didi_10242]

I have been preparing interviews for data scientist positions, and the coding part of the job is not too easy for a person without a computer science background. I was struggling in understanding the recursion function for a really long time, and this is the first time I finally understand it intuitively after watching your video. Thank you so much! Your call stack illustration helps a ton!

[@BackToBackSWE]

Thank you, glad you liked it 😀 Do check out backtobackswe.com/platform/content and please recommend us to your family and friends 😀

[@jiadongyu131]

I found myself smiling as I watched this video because your passion and enthusiasm really shone through. Great explanation and good work!

[@BackToBackSWE]

Great to hear!

[@JakealiciousAndBros]

I’ve been struggling with DSA, but the way you taught this really opened my eyes. I’ll admit, I watched a few parts several times, but I love your energy and will definitely be returning for future problems!

[@VickyMei]

lol I love how you are so enthusiastic about this :D

[@BackToBackSWE]

ya

[@bn2005]

thank you for framing this as pointer manipulation instead of "moving nodes" like so many tutorials do

[@BackToBackSWE]

sure

[@nicolerussack9800]

Idk how you can be so excited talking about recursion but it's making me excited!!!

[@Sheldor.The.Conqueror]

You explain recursion like no one in their wildest dreams can even think of !!!!

[@AndrewWheelerJr]

Kind of makes me miss college. I would also get really excited when I finally understood something and was explaining it to someone. Thank you for helping me understand it.

[@BackToBackSWE]

Sure. great.

[@jinhuang7258]

Explains recursion so well. Thank you.

[@maricampbell8240]

Thank you! The iterative explanation and diagram was so helpful for me. I was able to implement the function without looking at a code example, but from imagining the diagram you created.

[@BackToBackSWE]

nice

[@uditgaba1450]

saw this video for reversing a linked list recursively . Helped me a lot . Thanks man !

[@BackToBackSWE]

great - sure

[@alhaithamaljabri6126]

OMG... Thank you so much for your amazing teaching skills! I am happily crying since this finally makes sense to me after all that struggle...

[@BackToBackSWE]

thanks and nice haha

[@serrasilva7316]

I love your enthusiasm. It makes it so much more fun to learn.

[@soujanyayprabhakar]

I watched so many explanations regarding this i could not understand but i got an idea about this by watching your video . Kudos !!!

[@BackToBackSWE]

thanks

[@rikki146]

bruh this is a treasure on youtube. thank you!

[@annawilson3824]

10:40 so we have head that points to 3 and new_head(reversedHead) that points to 4. Overall, since each time we have a function call with a new/subsequent head, once we start returning, the head is going to be updated for each call in the reversed order once we propagate back/up the stack, but new_head/reversed will stay the same (we set it value once when we reach the depth of the calls) and always points to 4, so we return it at the end of the whole function.

[@pranavbhat92]

The intention & intensity with which you explain is commendable. You deserve more subscribers. I subscribed! 😊

[@LesAxolotl]

Hey man, thanks for this video. It's such a simple an elegant solution. I spent the last 12 hours trying to solve it myself (not too smart really) and finally gave up and came here. Your explanation is so clear. Cheers!

[@aniarablechannel4668]

Just because you couldn’t solve it doesn’t mean you are “not too smart”. It could just be a difference in coding experience. I wouldn’t get down on yourself. You’re already doing great and setting yourself up for success by working hard to get better and watching videos like this!

[@teensymarie]

I can only hope that one day I can explain this with as much excitement and clarity as you do.

[@zahranajib5528]

Ahhh please make more videos!!! You are such a lifesaver I swear. Watched your video like 5 times to really understand the concept. Maybe on recursion and more data structures. Also, a suggestion, try to talker slower :)

[@BackToBackSWE]

Thanks and we will

[@anthonysoffice9367]

you explanation on recursive method was pretty clear

[@BackToBackSWE]

great glad it helped

[@Roover_sa]

Brother no words for you . i am stuck at temp->next->next but you nailed it with the example "Let me Add myself" Lot's of love from india

[@BackToBackSWE]

hey

[@eg816]

you're so good at explaining!. thanks !!

[@BackToBackSWE]

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[@alpavaidya412]

If I had a teacher as enthu as u bout teaching I would have been better programmer today...appreciate your efforts

[@BackToBackSWE]

thanks

[@roliverma5851]

Best video on recursion I have ever watched

[@anupamdungdung9417]

Sir the way you give so comprehensive explanation... I love it!

[@deepeshrathod2044]

Damn! this is the best video I found. It just cleared all my doubts for reversing a linked list recursively. Thanks for the video.

[@joshj8459]

Yea I subscribed. You had me on the edge of my seat the entire video like I'm watching a suspenseful movie.

[@BackToBackSWE]

haha thanks for the sub

[@fantasy9960]

this is the best explanation for listNode reverse! Really appreciate it !!

[@yuselina8769]

Really love your illustration! Thank you!!

[@ashwinvarma9349]

I came here for the recursive method and the explanation was great! keep it up!

[@BackToBackSWE]

sure

[@cf921]

This guy explains reversing a linked list like playing basketball with all the shoes' sound lol, love your enthusiasm ;)))

[@BackToBackSWE]

hey

[@spiritualgyanhindi2681]

Thnx! Finally, I got this logic of returning back after top to bottom😄

[@ApexPlayground_divine]

Bro thanks alot man I final understand this stuff, thanks so much😭

[@kanishkarao979]

Finally a simple explanation. Thanking God for creating you 😁 😁 😁 😁 😁

[@taesookim531]

Thank you,, NEXT

[@BackToBackSWE]

hahahahahahahahahaha. Best comment on this whole channel. I love you.

[@HopingforPower]

One of the more clear explanations of this god forsaken problem. Thank you

[@ri7_cars]

Thanks, finally understand the recursive solution. The explanation of call stack really helps.

[@BackToBackSWE]

thanks

[@sky76570]

12:58 Hahaha, explanation with synchronized movements is hilarious bro. Respect.

[@BackToBackSWE]

ye

[@gazalaparveen1254]

This is literally the best explanation I have come across🙌

[@BackToBackSWE]

Thank you, glad you liked it 😀 Do check out backtobackswe.com/platform/content and please recommend us to your family and friends 😀

[@kevintravelsgram]

I thought the recursive way was really confusing so I had to look it up on KZbin. Really glad I found this video. Amazing explanations!

[@BackToBackSWE]

haha nice, wassup

[@cappuccino2345]

Thanks buddy, I like your explanation better than other's.

[@BackToBackSWE]

nice

[@Mines2013]

Never seen anyone this excited about reversing a linked list, haha

[@BackToBackSWE]

I am a lively guy

[@supamdeepbains5172]

my homie always there to help me with data structures

[@himanshusarad6491]

tysm man ...you literally nailed it with this explanation .....finally i understood how to do this now.

[@andywu9774]

This guy is probably the most passionate CS guy in the entire universe!

[@aleman87]

Very good explanation. I've watched a few of your videos and all of them so far have been easy to follow and does a good job of explaining the approach.

[@BackToBackSWE]

thanks, welcome to the tribe 🍖

[@leetsai6220]

Watching your explanation and just the passion that you put into these videos really helped me remember the nuances of this problem.

[@BackToBackSWE]

great

[@mingyuetang7041]

Great explanation!!! gonna use your videos for interview prep. Many thanks 🙇

[@BackToBackSWE]

great!

[@mase-ob1vf]

Paid for a DSA course on Udemy and ended up have to KZbin because the explanations were trash. You explained it beautifully and made it incredibly easy to understand. Before finding this video I was dumber than a rock.

[@BackToBackSWE]

Glad it helped

[@jake18111996]

every one is asking how he is so enthusiastic but my mannnn took a preworkout and he is getting the pre workout kick!!!!

[@chamnil8666]

Thanks Handy Dandy,now i can reverse a linked list,have a blessed day.

[@BackToBackSWE]

great

[@helenashatalova7828]

Finally, I got it! Thank you so much for your video! Your channel is a hidden jam!

[@BackToBackSWE]

thanks!

[@firstcomesrock8593]

this is the best explanation of this concept

[@BackToBackSWE]

Hahaa yay

[@annawilson3824]

Awesome! One thing missing is head.next = null, because that link is not needed anymore.

[@anmolsharma9539]

The time i see that you had made a video on this i know that my doubt is going to get resloved before the video gets over and it happened :)

[@samuel2318]

really love his way to explain this question🤣 he is so enthusiastic and energetic!

[@snake1625b]

This is why online learning is so much more Superior to in person lectures. In person it would probably go way over your head. But on KZbin you can pause and rewind as many times as you want until it clicks

[@BackToBackSWE]

haha nice, this video is old and not that good

[@snake1625b]

@@BackToBackSWE it's pretty good. I still find the recursive part a bit confusing though. I know it's common for employers to ask how to reverse it iteratively but do you think it's common for them to ask to do it recursively?

[@Ryan-xb1ry]

I finally understand this. Thank you.

[@BackToBackSWE]

Thank you, glad you liked it 😀 Do check out backtobackswe.com/platform/content and please recommend us to your family and friends 😀

[@user-ri7fo6tp5e]

Great Teacher man! Finally got the recursion when you could help me visualize going downwards then backup. Thank you man!!

[@BackToBackSWE]

Thank you, glad you liked it 😀 Do check out backtobackswe.com/platform/content and please recommend us to your family and friends 😀

[@fromscratch8774]

Best Explanation, thank you! I think you have to write the recursive version yourself and draw the nodes to really get it.

[@BackToBackSWE]

Yes

[@iraisvalenzuela6147]

Thanks for the video! You simplified this so much for me!

[@MaminaZvezdochka]

Oh your energy 🔥🔥🔥 I was going to sleep but now I will have a big brain time evening 😆😆😆 thanks so much!

[@BackToBackSWE]

Haha so glad!

[@jacktrainer4387]

These videos are amazing. You're a phenomenal instructor.

[@BackToBackSWE]

Thanks man! subscribe to my DSA course for some amazing content b2bswe.co/3HhvIlV

[@TadiwanasheNyamapfene]

Absolutely the best video to explain this. Just took away all my frustration lol!!

[@soradev5386]

It took a while to sink in, but thanks for this detailed explanation to the problem. You killed it

[@BackToBackSWE]

thx

[@kunalkeshavsinghsahni6861]

Thanks for the beautiful explanation

[@BackToBackSWE]

sure

[@mohanm8556]

great explanation....I am able to visualize the recursion while you explain

[@BackToBackSWE]

Thank you, means a lot 🎉 You can also check out our free DSA course - backtobackswe.com/

[@skyechapman6595]

Ah thank you! I'm currently working on this question for school and my dumb mind wanted to approach this by nesting an if inside of a for inside of a while, but trying to find a way to decrement the count lol. Lifesaver!

[@raht9578]

now THAT is how you explain recursion

[@jbphoto7]

Finally! A perfect explanation.

[@TCErnesto]

I really liked your explanation on the recursive method bro thanks

[@niharikayerramsetty8582]

i have seen many videos but urs is awesome and the best

[@BackToBackSWE]

thanks.

[@acupof_joe]

dude this guy is awesome i wish he was my professor

[@xingjianwang1894]

Explanation is crystal damn clear.

[@BackToBackSWE]

thx

[@Polarwhite43]

Best explanation out there Thanks man

[@BackToBackSWE]

thanks

[@ankurjain8339]

Such a thorough and simple explanation. Thank you!

[@BackToBackSWE]

sure

[@Bhavin-Desai]

Best explanation I have seen so far for reversing a singly linked list .

[@BackToBackSWE]

thx

[@indranilchakraborty5930]

Love from India..🇮🇳🇮🇳

[@BackToBackSWE]

thanks

[@ExplorerSpace]

omg you are a life savior

[@Max-zf5ot]

How can someone thumbs down this video !!! Amazing effort and urge to explain the solution !!!

[@BackToBackSWE]

thanks

[@joehaynes7092]

Had to rewind a lot but first video that worked to understand it :)

[@bronzebond4869]

You do a great job fam. Thousands of us appreciate the help. Thanks again

[@ubohllc6587]

Great Job and great explanation. You take so much effort to explain. Thanks so much!!

[@BackToBackSWE]

sure

[@sanghunlee6825]

Life saver bro Thanks for your kind explanation

[@prathyyyyy]

THE BEST VIDEO ON KZbin !!!!!!!! IM IN LOVE :)

[@mamoodshaban3119]

That was really helpful man. I'm grateful! Keep up with the good work!

[@BackToBackSWE]

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[@nuke4496]

took me sometime for me to digest. thank you.

[@pankajmenaria3230]

best explanation of reverse singly link list

[@pankajmenaria3230]

Do you have any DSA course ?

[@labgeek1559]

love your videos, keep up the great work.

[@BackToBackSWE]

thanks

[@tienduong7729]

My man big on energy. Love it!

[@holyshit922]

My way to do it Initialize reversed list //List will be created from existing nodes there is no need for allocating memory for new nodes While original list is not Empty do Pop node from the original list Push node to reversed list return the reversed list

[@BackToBackSWE]

ok

[@sj9851]

I think it's still not clear enough. Perhaps if you could explained how memory location worked. x = 'value' y = x delete x; y === 'value' // returns true I think many people are confused of what reassignment means here in your algo. For example, what does prev = cur mean in your explanation? Why prev mark is moved to cur loaction when cur is assigned to prev? Many people might think "cur" mark should move to "prev" location in your graph if they don't understand how memory location works.

[@diegoi1313]

Thank you for this well informed video!

[@lukehatcher98]

incredible explanation. THANK YOU