🚀 neetcode.io/ - A better way to prepare for Coding Interviews

@oanamanaljav

3 жыл бұрын

Seems like the code is not working. Showed me the wrong result when compile.

hearing "hey guys i'm still unemployed so let's solve a leetcode problem today" and knowing you became a software engineer at google is so real and inspiring bro, thanks

@alwin5995

7 ай бұрын

Bruh he left job at amazon, and decided to voluntarily be unemployed. Dude's been a genius all along.

"hey guys i am still unemployed so lets solve a problem " this is savage bro

@farnazzinnah8541

2 жыл бұрын

he earns fro youtube tho

@samirpaul2

2 жыл бұрын

😂

@computergeek5657

2 жыл бұрын

KZread hired him

@neerajmahapatra5239

2 жыл бұрын

Now he is at google

@omkarjadhav8482

2 жыл бұрын

💯😂

I get so inspired/motivated when you mention unemployment in your old videos because of where you ended up

that intro hit me different

@NeetCode

3 жыл бұрын

lol

I've been watching your solutions for a while now and I'm just so happy that I finally started to solve problems like the way you do. Thank you so much!!

That beginning took me by surprise, instantly made my evening better. Thanks

Awesome, I love how you dealt with all the edge cases without cluttering the code

"hey guys i am still unemployed so lets solve a problem " this one cracked me up because right now all your efforts paid off and look back, we all have been there..ah what a journey!!!

Congratulations that you are now employed!! Happy for you!

i'm amazed at your ability. it's the nuances in the code that's the hardest to figure out. kudos to you.

By far the best explanation of this problem I’ve seen 👏 Thanks for sharing

Love how you started the video! xD You made my life easier by posting these videos. Great work! :) :D

Excellent! Clear and plain explanations, and it's so much cleaner when hand mark-up is by pen instead of by mouse. :) This is linked in LeetCode as "optimized solution explained" on the problem itself, but it'd be faster to take: carry = val // 10 val = val % 10 ...and make it instead: carry = 1 val = val - 10 The modulus approach is fantastic for expanding our algorithm to support adding up three or more arrays, but in our use case carry will always be 0 or 1.

@stementhusiast816

2 жыл бұрын

You would require 'if' statements. if val >= 10: carry = 1 val = val - 10 Which would reduce the elegance of code

@khatharrmalkavian3306

2 жыл бұрын

Nothing about this problem is elegant or worth optimization.

Couldn’t have solved this without you. Thank you so much

@alok7485

2 жыл бұрын

Can you please explain what will be the time complexity and space complexity for this piece of code in example?

Explanation was crystal clear and helped me solve the problem super quick. Thanks!

Thanks for making this. Trying this problem is the first time I've ever tried using a Linked List, so this helped solidify the solution LeetCode provides.

@alok7485

2 жыл бұрын

Can you please explain what will be the time complexity and space complexity for this piece of code in example?

Wow, this was very well explained!

The intro slapped me back into reality. As always, thanks for the awesome explanations 😄

thanks for making these videos man, your awesome

Haha, now you are so employed! Thanks for these great contents!

So simple, thank you. I was casting the linked list values to strings and reversing them, then casting them back to ints and adding them... needless to say I was making spaghetti. Your example is very clean!

@prudvi01

3 жыл бұрын

lol that was my initial solution as well! got dirty real quick

@liferayasif9382

3 жыл бұрын

I did same, thanks

@UnknownSend3r

2 жыл бұрын

@@prudvi01 I used an if statement inside a while loop, would that be wrong even if it works, if not what's wrong with it ? As in does the solution have to be a linked list.

@BromaniJones

2 жыл бұрын

I did the same. I'm not convinved it's any worse than the solution presented in the video. looping through two linked lists (and a third for the output) is O(n) time complexity.

@gustavotelez9795

Жыл бұрын

def addTwoNumbers(l1,l2): l1.reverse() l2.reverse() l1s= str(l1) l2s= str(l2) l1s= "".join(l1s) l2s= "".join(l2s) l1 = "" l2 = "" for i in range(1, len(l1s), 3): l1 +=l1s[i] for i in range(1, len(l2s), 3): l2 +=l2s[i] l1s=int(l1) l2s=int(l2) res=l1s+l2s res= str(res) res= list(res) res.reverse() return res

Dude, thankyou for this solutions. They are helping me alottttt! Also, if you could please make a video on intersection of two linked lists

@alok7485

2 жыл бұрын

Can you please explain what will be the time complexity and space complexity for this piece of code in example?

Thank you !! I finally understand it now

Great video and great channel I am very excited to discover this channel I hope I benefit from this channel a lot .Thanks a lot😊

Man I was super stressed out solving these leetcodes, but the " Hey I am still unemployed" made my day! LMAO

Better explanation than the official solution explanation.

You are best. I always pause ads blocker for you.

This intro make this video my favorite one 😂. Could be a useful cue to remember the solution in an interview even.

its interesting how you build the answer after the dummy node and return the answer. Its not like the test cases can detect the dummy node

This solution is so elegant.

"you probably do but you might think you don't". Haha, thanks for the encouragement.

thank you for the explaination :)

I traversed through both linked list and got the actual numbers, added them, then created a linked list with the result's digits as nodes.

@inspisiavideos8542

2 жыл бұрын

hi, Please let me know. Why is the value divided by 10? I'm learning how to code and I don't know where he got the number 10? (on minute 7:29)

@danielwilczak7833

2 жыл бұрын

​@@inspisiavideos8542 You divide by 10 so that you can add it to the next number which will be in the next 10's place. For example: if you took 25 + 26 if you add 5 + 6 and then divide by 10 you'll get 1. So i take my one and add it to the next 10's place which is 2 + 2 + 1 that i got from carrying the number which will total 51.

@inspisiavideos8542

2 жыл бұрын

@@danielwilczak7833 Thank you so much!!! I got an internship during this Summer as QA and just finished it but I asked for an extension and if I could get it this time as Dev. They said yes. I have coded before with courses on how to make websites but I have never done code questions. Basically this next week is my first week. It’s so hard to get a job so they told me that they don’t have entry level positions and senior positions are more than likely ending up on people who are already in the company. So basically I’m learning as much as I can during my spare time to then perhaps they let me stay after the internship extension ends by the end of the year.

@philhamlin7935

2 жыл бұрын

@@inspisiavideos8542 Congrats on your internship! Calling out 10 as a "magic number" is really great - bare numbers with no evident explanation can cause a lot of confusion in code, so 10 could be a constant called NUMBER_BASE since we're just using decimal notation here. For extra fun, make it not a constant, and adapt the algorithm to work in number bases other than 10!

@inspisiavideos8542

2 жыл бұрын

@@philhamlin7935 hey thanks! My internship was supposed to end in August but was extended to the end of December. I’ve been applying to other companies but nothing yet even though I have projects on my portfolio. My internship manager told me to stay alert when an opening occurs and apply. 2 positions opened and I applied there this week. Hopefully they’ll let me know and I be ready for a test code. The company has many teams so probably the person who sees my resume doesn’t know me yet.

For some reason it was extremely easy problem for me, first time that I just saw the solution instantly in full (unlike all “easy” ones before) and was so surprised of everyone’s animosity to this problem, lol.

great explanation!

Only Platform I choose for any coding explanation

I cant figure out how does cur work. If I print id(cur) == id(dummy) it's true, but if i print cur and dummy inside or after while cycle the output is different. Tell me please what's going on or What should I google to clarify that ?

This is the way I learnt about pointer, I can't believe it

so do we have a first node that is just null in all of these

wonderful explanation

LOVE you my GURU your awesome!!!

what's the function of next and val do?

Can someone explain the dummy listnode and how changing in cur changes dummy?

I did 'print(Solution().addTwoNumbers(l1,l2))' and got error "list object has no attribute 'val'... how do I fix it?

A complete beginner question, how to call and declare the inputs for addTwoNumbers function, just to test the program !

NC: You do probably remember how to add two numbers together Me: You severely overestimate my abilities

I am very happy for you that you are employed at Google now. 😀

you are the legend

Can someone explain why we don't use the first dummy list node? Why not use dummy.val and assign?

@gimmeadollr

Жыл бұрын

I think it's because we want the logic to be "the next thing is ___" for every iteration, so we make a dummy list node and immediately start with our logic (the next thing for the dummy node is ___). If you use dummy.val, you have the first step do the logic of "the value here is ___" and then the later steps are "the next thing is ___" which is more inconvenient to write. That's how I thought of it, not sure if that's the right way to think about it.

Inspirational first line

A little confused,how are we adding in reverse order? we're just adding v1 and v2 which is normal addition isn't it?

@khatharrmalkavian3306

2 жыл бұрын

The digits are in reverse order.

I was really close to the solution on this one. I had an extra node at the end because I was creating my node in cur instead of cur.next(). Slowly getting better at these

"hey guys i am still unemployed so lets solve a problem" mans representing his entire audience 😂😂😂

@NeetCode Could you please explain the time complexity of the problems you solve? It will be really useful for us.

@wlockuz4467

2 жыл бұрын

For this one it should be O(n + m), where n is length of first linked list and m is length of second linked list.

@predatorgaming895

2 жыл бұрын

@@wlockuz4467 no bro... Either O(n) or O(n+1) where n is the length of linked list which has more nodes

@alok7485

2 жыл бұрын

Can you please explain what will be the time complexity and space complexity for this piece of code in example?

@likkiii07

Жыл бұрын

@@alok7485 Time complexity will be O(max(n, m)) and Space complexity will be O(max(m,n))

nulll and zero are different, you should instead append the while statement to while l1 or l2 or carry>0

@jaspreetsahota1840

7 ай бұрын

In python, 0 evaluates to its Boolean value (False) in a conditional clause. So it's fine to just have carry.

@TheEllod

7 ай бұрын

@jaspreetsahota1840 good to know!

If the person teaching these is unemployed what chances do we have...

this explanation is much better than the leetcode editorial

@tsunningwah3471

7 ай бұрын

can anyone tell me why we're returning the dummy.next and not dummy itself? wont we be able to access every other element if we just return dummy?

I'm really proud of mylsef. I finally managed to solve a medium problem by myself, although my solution was slow as hell xd

Can you explain how can I call the l1 and l2 listnodes in the addtwonumber function to test?

@crosswalker45

2 жыл бұрын

it's a bit compicated to explain it in words. I would rather suggest you to watch the videos on how to create linklist object and other related problems ( which aren't directly given into the function like this leetcode problem)

@mugilmithran6955

2 жыл бұрын

@@crosswalker45 hi, thanks a lot man.

I was able to solve this one, but did not think of dividing the current sum by 10 and using Math.floor() to get the first digit as the carry number, and then using modulo to get the second number aka the current sum. So darn clever! Instead I converted the sum to a string and grabbed the values by index.

great thank you

Thank you !!!

@tsunningwah3471

7 ай бұрын

can anyone tell me why we're returning the dummy.next and not dummy itself? wont we be able to access every other element if we just return dummy?

I got some errors when I ran your exact code. Is your solution missing the case when the highest position creates a carry of 1?

@yinglll7411

3 жыл бұрын

you might have missed the "+ carry" bit when summing up the "val"

@dorb1337

Жыл бұрын

while l1 or l1 or carry:

Beginner question- I wanted to build test cases before diving in. I went off on a tangent to construct ListNode instances- which I needed as inputs to LeetCode's provided addTwoNumbers interface. I prepared all my tests before even thinking about the solution. Is this wrong? I don't see anyone doing this. Is this wrong or shouldn't we do TDD?

@mrunfunny

2 жыл бұрын

This is a perfectly valid strategy but it's time consuming and hence not popular in CP community.

Thanks

I am so happy that LC decided to give us reversed lists for this problem

Can someone explain what happens inside the stack with the statements "cur = dummy" and "return dummy.next"?

@yipyiphooray339

Жыл бұрын

curr is what you use to traverse the dummy linked list, while, "dummy" will always point at the head of the linked list. Since you're returning "dummy.next" you'll be returning the head of the resultant linked list.

I don't understand what's going on with carry. Wouldn't always be a left over number there by the time two get to the second digit in the list nodes. First time through: val = 2 + 5 + 0 carry = 7 // 10 Doesn't that leave carry as .7 when we get to the next digits? I'm very confused.

@aiml66_bangerashashankchan81

Жыл бұрын

In Python, we can perform floor division (also sometimes known as integer division) using the // operator. This operator will divide the first argument by the second and round the result down to the nearest whole number So, 7 // 10 = 0

When was dummy head ever updated in the code? Please help!

KZread hired u👍

BRO! UNIQUE..!! "Hey Guys, I am still UNEMPLOYED so let's solve a problem!" Lmao!😂

Wow this is so clean✅✅ I brute- forced my way to this problem and it's functional but really ugly 😀

Can anybody explain me? In the begin we wrote "dummy = cur". After that we updating "cur" in the while-loop. But we don't update "dummy". So how "dummy" is updating together with "cur" if we don't redefine "dummy = ..."

@joya9785

Жыл бұрын

Exactly my doubt!!!

Can Some please explain why the dummy is still getting updated when after the first iteration cur is updated to a different object. newNode = ListNode(columnSum % 10) curr.next = newNode curr = newNode

@robwalsh3858

2 жыл бұрын

At the start of the loop cur = dummy. On the first iteration you are assigning cur.next (aka dummy.next) with the first digit of the solution. So now dummy.next equals the head node of the solution so at the end we return dummy.next. dummy.next will always point to this head node no matter what cur gets changed to.

@ai4sme

Жыл бұрын

Hi Sajith, Here a good explanation: stackoverflow.com/questions/58759348/when-does-a-pointer-to-a-linked-list-change-the-actual-list

@drainedzombie2508

5 ай бұрын

@@ai4sme Thanks for this. TIL python variables are essentially references/pointers to objects i.e. class instances.

I have interview on 21st March, there is no way I am gonna pass :( This level of programming is going above my head

@supriyamanna715

2 жыл бұрын

kaya hua? Pass kiya tumne?

@alok7485

2 жыл бұрын

Did u pass?

@Davidsito44

11 ай бұрын

how did it goes?

Hey, it is showing the time limit exceeded! Please help!

@sumanth5087

3 жыл бұрын

see in discus section there u can see many solutions

Hi. Can someone help me understand how and why there is l1.val? I thought l1 is a list which is [2, 4, 3]? How does l1.val calling integer 2? Or it's from ListNode class? I'm very confused.

@smilenpassion

Жыл бұрын

if you see the ListNode class there is a val, which is used to access the int values of the nodes so it is used as node.val (in this case l1.val) hope it helps

@roy761017

Жыл бұрын

Hi @@smilenpassion thank you for your respond, but I am still confused. Class listnode is not inheritance under class solution. How can class solution call any object from class listnode? Also, even it can call the object from listnode, shouldn't be v1 = self.val if l1? Or set the self.val to l1.val? Thank you again for helping me to understand it

"Hey guys, I'm still unemployed.." Many kisses for you neet! you make me laugh.. And relax... To the best ASMR Channel OUT-THERE!!!! Please go back to this microphone and keyboard, and relaxed voice!!!!!!!!! damn I enjoy this

can anyone tell me why we're returning the dummy.next and not dummy itself? wont we be able to access every other element if we just return dummy?

@tsunningwah3471

7 ай бұрын

yes i have the same question too. I thought dummy itself is the real list

@m0sh3

7 ай бұрын

@@tsunningwah3471 dummy is initialized to default value of 0 for the purpose of having an initial node to attach everything else to. dummy.next is the real start of the summed list.

@tsunningwah3471

7 ай бұрын

@@m0sh3 thanks got it！

Stupid question but how does "dummy" get updated when all code changes are done to "cur"?

@chillcoder

Жыл бұрын

Both dummy and cur are both pointers to the same list, but serve different purposes: We are using dummy to point to the start of the list and cur will be used to add additional nodes + move to the latest node in the list.

To deal with edge case just before . return dummy.next write If carry==1: cur.next= ListNode (1)

understood

This was hard argh I had no idea how to implement carry. Thank you for explaining! I don't understand the dummy node part. can we not use a dummy node? Why not use curr and return curr?

@austinpatton3771

Жыл бұрын

You could, but in my experience the dummy node generally makes building the linked list easier since you can loop through it with less conditional statements. If you don't make the dummy node, you would either have to have a separate if statement to check that our starting node is not null or find some other way to do a one-off initialization of the list. With the dummy node, you can process the nodes each time without having to worry about if it's your starting node or not.

Why are these things so difficult 😣?

Why can;t we simply reverse two lists first, sum them and then reverse an output?

My sentiments exactly. If NeetCode is unemployed, what chances do we have...

@NeetCode

2 жыл бұрын

Well.. not anymore :p

@dr.merlot1532

2 жыл бұрын

@@NeetCode In my heart and mind, you are still unemployed.

At the start of the loop cur = dummy. On the first iteration you are assigning cur.next (aka dummy.next) with the first digit of the solution. So now dummy.next equals the head node of the solution so at the end we return dummy.next. dummy.next will always point to this head node no matter what cur gets changed to.

@alicia8170

Жыл бұрын

I quote your response to ask the question further. As I understand, cur = dummy means let cur be dummy, but they are not the same one. I still don't understand whey cur.next will change dummy.next. Did I miss anything? Thank you so much!

@oliverbao4925

6 ай бұрын

@@alicia8170 hi yeah i'm wondering the same thing - although we didn't reference dummy at all or change its value, it gets built on as we change cur and cur.next - is this a python binding or pointer issue?

0:00 Lol now you're at Google. Here I am just trying to get Amazon or Microsoft now. Awesome solution, I managed to actually solve this one myself but wanted to see your way of doing it, much cleaner. Thank you! Liked!

"I am still unemployed" Not anymore!

Here after when you got job in Google.... congratulations:)

how dummy variable is updated through while loop?

@shivakhatri3271

Жыл бұрын

did you figure it out?

@-Mohamed_bayan

11 ай бұрын

Learn how linkedlist words

How to achieve time complexity o(n)?

@likkiii07

Жыл бұрын

You can't. It's always going to be the length of the larger list. Hence O(max(m,n))

This code only passes 1365/1568 test cases. Update needed.

this solution gives TLE (Time Limit Exceeded) any other solution?

@NeetCode

Жыл бұрын

Most likely you have an infinite loop somewhere, are you updating your pointers?

gold

i solved it using more memory but it eliminates thinking about edge cases: nums1, nums2 = [], [] cur = l1 while cur: nums1.append(cur.val) cur = cur.next cur = l2 while cur: nums2.append(cur.val) cur = cur.next nums1 = nums1[::-1] nums2 = nums2[::-1] num1 = int(''.join(map(str, nums1))) num2 = int(''.join(map(str, nums2))) vals = [] number = str(num1 + num2) for c in number: vals.append(int(c)) dummy = ListNode(0) cur = dummy while vals: cur.next = ListNode(vals.pop()) cur = cur.next return dummy.next

could have reduced these statements within single block, otherwise awesome explanation thank you if(l1 != null){ v1 = l1.val; l1 = l1.next; } if(l2 != null){ v2 = l2.val; l2 = l2.next; }

Why can't you reverse both list and just add the two reversed list together?

Thank you for a quick solution! However, it is not space optimized as per the requirement: Ignoring the allocation of a new linked list, try to use constant memory when solving it. Would be better to add summation digits in longer LL.