LeetCode 36. Valid Sudoku (Algorithm Explained)

[@calfland79]

at 9:08 when he said it is not difficult, my face turned into red. If I've never saw this kind of solution before, I would be doomed in a interview :)

[@Kitchen-Raccoon4572]

lol he says that for so many problems and I get kinda sad when I hear that :(

[@CoolnesXcore]

@@Kitchen-Raccoon4572 Don't get sad... Nick is a little arrogant plus he has been doing this for a while. Practice makes perfect!

[@Turnpost2552]

What most developers mean that it is relatively easy. Like it is relatively easy to get a phd than to become President. Both are exceptionally hard to get though.

[@tasneemayham974]

For real!!!!! Sheesh I spend 2 hours just to figure out what is happening in my code!!

[@impos1ble32]

The solution with the single string HashSet looks like pure genius to me. Great video!

[@samwilson4597]

big brain solution

[@Ingenius3]

Huh, the advantages of knowing your data structures and methods...I've spent 10+ hours on a similar sudoku problem and been trying to use only arrays and 2d arrays combined with control statements, and it's been a nightmare to be honest, and now I see this and I really think I gotta learn some data structures, it's ridiculous how fast you can come up a solution like this

[@webknowledge9989]

If you feel bad...don't. He spends a lot of time beforehand looking at different solutions, trying to come up with his own solutions, improve it and improving the different solutions he saw. And then, choosing the best one. This is pure hardwork.

[@feeaven]

This honestly was the simplest and best solution i've seen.

[@shusenacademy]

Readable code is much better than smart code. Your solution is understandable. Thanks.

[@johnhappy9230]

bro you have the best explanation that i've seen. Thank you so much

[@pradeepanand5296]

This is lit. No words. I solved the arcade section of the sudoku by using two hashset one for row and one for column. Never thought this could be the way to optimise the code.

[@ruchirai5775]

One word - Genius

[@rutustup396]

The answer were already on leet code. 😅

[@sicals1720]

That moment when he first type the input for strings hash set is just simply mind blowing like "OMG off course it will works"

[@Last_Resort991]

It will work better than your grammar teacher.

[@a.human.]

@@Last_Resort991 when the grammar nazi doesn't know grammar himself lol

[@khanshadab806]

Also, you could remove the big 'if' from the 'for' loop and just check if the size of the set is 3*(Number of non-empty places in the board) after the loop. If it is not, the answer is false.

[@danieljakel5105]

You could also make a list of 81 list with 9 entries each for every field and number that is possible. Then you write a algorithm that cross out each number from the nine possibilieties that has a double in line, colum or quadrat. When all numbers cut one in a list are crossed out, you have found a new one that you can use to delete the other list of posibilities. If each list have just a number its solved!

[@PrinceKumar-el7ob]

Exploded my mind what a brilliant way to write aesthetic code man !!

[@lugiadark21]

This trick is INSANE!!!! I hope I never get asked a problem like this lol

[@shubhamkhurana7545]

This was a really cool solution Sir, so we can also implement even a string matching algo using string datatype hash set. This problem really teaches a cool concept!! Thank You Sir!!

[@fabusuyiayodeji7016]

Wow! This is the most intuitive solution I've seen to this problem

[@enthusiasticsimple901]

Great Solution!! Thank Nick for posting these videoss

[@aba0101]

Brilliant!! Just to make sure, is the time and space O(1)?

[@osamabassam7517]

A clever solution, but the simple solution (Validating rows, columns, and boxes seperately) is way more faster, for me this solution beat 100% of java solution in term of time, the solution in the video beat 22% only (Which is because of strings hashing I guess).

[@jordananders8525]

Wouldn't this fail if one of the 3x3 squares looks like 1 2 3 4 5 6 7 8 9 and if there is another 3x3 square to the left or the right of the first 3x3 square that looks like 7 4 5 8 2 3 6 1 x where the x denotes an empty square, then this is an unsolvable Sudoku puzzle.

[@decisive5760]

It's doesn't matter if the sudoku puzzle is unsolvable. This leetcode problem is only checking for the three rules in the description

[@seyikareem8052]

Curios if it is possible to extend this solution to solve the Sudoku solver problem...

[@soumi7356]

This was a very different approach !

[@DeepakAnand-x3f]

Rather than using 3 hashsets using a single hashset was brilliant .

[@lifeofme3172]

WOW amazing solution loved it keep it up dude!

[@Jdudeo]

The string concatenation allows using only one map, but what is the point of this? It's nifty, but I don't see a real reason to use this from a practical standpoint

[@iamloking]

Loved the solution!

[@dangbey4822]

genious, thank you very much

[@orangetree2104]

Trivia : Nick White still has the hat used in his profile picture, and actually went to Columbia

[@velmuruganr9321]

wow..that blew my mind...I mean wow... Im speechless

[@emanuelcristutiu5854]

Really good explanation, thx mate!

[@tushar_agarwal_it_2nd_a_477]

Can anyone give the cpp solution of this question,I am having some issues in my code.Thanks in advance:)

[@suryakumar-ow8bx]

its showing unexpected return value for return false line... wat to do

[@Nickel80]

What is the runtime for your solution? Is it O(n^2)?

[@praharsh_bhatt]

Yes.

[@divjyotsinghkhanuja1546]

It is O(1). The for loop will always run for 9x9 grid irrespective of input if thats how you came up with O(n).

[@divjyotsinghkhanuja1546]

@wapanapoli How can the grid size change lol please explain

[@Mark-tv1zs]

@@praharsh_bhatt The grid is always 9x9 (even says in the video), so the time complexity is O(1)

[@gopalchavan306]

wow Awesome, and I was spending hours to just solve this

[@AbhishekAnand92]

Brilliant solutions :D

[@vrindatyagi6744]

your vids are really helpful THANKS A LOAD

[@jz-nz6tq]

this method is fucking genius

[@NikhilTripathy]

WoW! That's so freaking cool..

[@CodeSuccessChronicle]

Me: (video put on mute until he claps)

[@inderjitsaini9303]

I tried doing the nested if with normal (seen.add) instead of (!seen.add), return true and return false in outside the for loops. but that doesn't work. Can you tell why?

[@vishnudarrshanorp3730]

in nested if statement you forgot to put ! symbol to check it..

[@stutipandey2564]

This is an awesomeeeeeee solution. I am mesmerized!!!! :)

[@kulaisaikumarkulai7319]

Great job

[@DavisTibbz]

Really? Snake_case in java? 😅 Anyway, cool content bro

[@ServantOfLordKrishna.]

this makes me look dumb

[@SmokyBigSmoke]

Thank you so much

[@WowPlusWow]

I did this in c++ and got only 6% faster. You also only got 22% This solution is a joke.

[@_sudipidus_]

Leetcode's system of calculating this is flawed.. I have seen same thing submission showing up as faster than (12%-80%) and then back to 12% within a minute.. (network connection or something)

[@sudhanshushakya4579]

Hye, can you show me your cpp implementation? I am having trouble doing it. I used unordered_set in place of HashSet.

[@bultvidxxxix9973]

Because this solution is really bad for performance. It's a nice quick solution in a coding interview, but if you want fast execution times, you shouldn't even think about generating strings to hash them... It should more look like this: public boolean isValidSudoku(char[][] board) { for(int i=0; i

[@yatinarora1252]

@@sudhanshushakya4579 ya that will be work fine for rows use ur unordered_sename[i].(arr[i][j]and column use ur unordered set name[j].find(arr[i][j]) and array element arr[i][j] and for boads use following as it is 9^9 matrix use arr[i]j].find(arr[i][j]*3(i/3)*(j/3))

[@Nathan00at78Uuiu]

I'm not understanding the logic and code for specifying a cube. It makes no sense to me.

[@decisive5760]

It's a 9x9 grid. A box is 3x3. If you divide the index of a row and column by 3, you get the box you're currently in.

[@MrSharmagaurav03]

This algorithm is wrong as it only check for first subset not all 9 subsets.

[@driveb6591]

Thanks for explaining. What's the time complexity?

[@justdevthings.7397]

O(n*n) where n is the size of the board

[@yatinarora1252]

LOL if we used three iterations instead of 1 iteration it will return 95% more faster solutions,in case of 1 iteration in c++ 35% only

[@anuraggorkar2299]

StefanPochmann sends regards ;)

[@arjunsuresh27]

worst explanation ever!! no intuition or walk through whats so ever cannot explain this in an interview!

[@somyasrivastava6315]

This is beautiful

[@rashedulislam9301]

nice explanation

[@karana2260]

does same number of elements in one hash Set or 3 hash set make a difference on memory usage? after all same units of memory is being allocated but pointers to each memory changes right? the type is same (char)

[@thewatcherlollol]

Well yea, you're using more memory

[@shravanipande7990]

Yeah, even I had the same question.

[@hopechan697]

really helpful thanks :3

[@swatiswagatika2017]

brilliant !!!!

[@bobered4911]

Nick no filter white

[@roshibansal2095]

You look like sheldon

[@pratheek5096]

Clever as fuck

[@jenblack8065]

Explanation according to discussion, no details. Not worth to go through.

[@ashwinishanbhogue2917]

F R E A K I N G GeniusSSSSSSSSSSS!! :D Mind=blown :)

[@amansaxena4446]

we dont know what u mean ,

[@freesoul2677]

It was a nice AHAAAAAAA moment =D Thank you!

[@charanpasupula3763]

Genius

[@SudeepDasguptaiginition]

excellent !!!!

[@algorithmimplementer415]

looks like you hate to use camelCase in the camelCase world of Java. :D

[@divjyotsinghkhanuja1546]

He codes in JS except for Data Structures I think thats where the underscores come from ;)

[@channelname8300]

WTF mannnnnnn...........................Destroyed it like a proooooo

[@nknidhi321]

Mind boggling🔥

[@ketansharma6955]

nice.

[@julietgeorge4858]

I hope you don't get tired of my comments but this is ridiculous(in a good way )

[@demidrek-heyward]

get it

[@YOUNGBLOOD-Alex]

WTF

[@vk1618]

Review

[@ankurkoul3731]

wow :)

[@Alison-yg6qs]

:-) !!! awesome!!!!!

[@ahmedfattah5879]

18

[@kedikebba6441]

Champ!

[@AmanRaj-tj7lj]

This does not work. Waste of time