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@meowmaple2 жыл бұрын
This is a clear explanation, but definitely still not the simplest. For me, the most straightforward method is to transpose the matrix and reverse each row. The code is simple and short. #transpose for row in range(len(matrix)): for col in range(row,len(matrix)): temp = matrix[row][col] matrix[row][col] = matrix[col][row] matrix[col][row] = temp #reverse for row in matrix: row.reverse() Accepted by leetcode.
@almasmirzakhmetov85902 жыл бұрын
excellent solution. By the way your solution is based on rotation matrix, right? For 90 degree, we have (x,y) -> (y,x) en.wikipedia.org/wiki/Rotation_matrix
@Rahul-pr1zr2 жыл бұрын
How do you even get the idea to transpose and then reverse? I agree that implementation is easier but the idea doesn't seem that simple.
@333jjjjjj2 жыл бұрын
@@Rahul-pr1zr You need to recall it from your linear algebra class. Good luck if that was more than a few months ago or never.
@peterpace33792 жыл бұрын
@@333jjjjjj for me it was a whole year ago lmao
@przemysawpobrotyn11952 жыл бұрын
I have another solution in similar vein. I came up with it by eyeballing the leetcode provided input/output samples and noticing that the firs element of the last row of the input is the first element of the first row of the output, the second element of the last row of the input is the first element of the second row of the output etc. thus n = len(matrix) for row in matrix[::-1]: for i in range(n): element = row.pop(0) matrix[i].append(element) also does the job ;)
@srinadhp3 жыл бұрын
This has been one of the toughest problems for me. Very hard to visualize and always used to make mistakes even after multiple attempts. The way that you explained the approach is THE BEST. You made it so crystal clear in visualizing the solution. Thank you so much!
@sidkapoor90852 жыл бұрын
I found it way easier, almost trivial when I stopped looking at the "2D matrix" and just at the input and output lists.
@caniaccombo1232 жыл бұрын
@@sidkapoor9085 mind blown
@markomekjavic2 жыл бұрын
I honestly think this is a Hard problem when it comes to implementation.. you can see the idea but coming up with the double pointer approach and a loop, thats a different story!
@huansir1922 Жыл бұрын
@@markomekjavic yes,coming up with the double pointer approach , it seems hard
@princeanthony8525 Жыл бұрын
Same here.
@doublegdog2 жыл бұрын
Just got an offer at amazon. Your videos rock and helped me out so much!
@NeetCode2 жыл бұрын
Congratulations 🎉
@MsSkip603 жыл бұрын
Thanks a lot for the content mate! No offence to others but I really like your clear accent and structured material which is easy to follow. Hope you keep up posting!
@d1rtyharry3783 жыл бұрын
Bro what an structured approach . Really loved your way of teaching man! You made it look so easy.
@NeetCode3 жыл бұрын
Thanks!
@xqfang31713 жыл бұрын
This is the best explanation for this problem. Crystal clear visualization, elegant code. Great job. Thank you so much for posting!
@NeetCode3 жыл бұрын
Happy it was helpful! :)
@parthpatel85322 жыл бұрын
Although this is a good way to do it, I found my way to be a bit simpler once you understand matrix manipulation. Rotating a matrix by 90⁰ is equivalent to flipping the matrix diagonally and then flipping it vertically. First try it out with paper, and once u get it, it's really easy. It doesn't save runtime or anything, but I find it easier in terms of code than to move 4 things at a time layer by layer.
@jim5621 Жыл бұрын
Brilliant idea. But this solution takes 2x time since you need to loop through the matrix twice. But the time complexity is still O(n) though. Good thinking!
@brainmaxxing1 Жыл бұрын
@@jim5621 "This solution takes 2x time" isn't actually true. Because of things like cache locality, where the elements that are in the same row will be closer to operate on for the CPU, it's not possible to say that the element-wise method is faster. The profiling method actually worked about 25% faster from tests on my computer!
@lottexy2 жыл бұрын
I gotta say your videos are amazing. I've been grinding LC for the past 3 weeks, I went from struggling to solve even 1 question on the weekly leetcode contest to solving 2 - 3 questions each week. Thank you so much. I've also and will always share your videos and excel sheet on reddit whenever people ask for leetcode tips. Oh and its abit late but congrats on the Google offer! I hope to one day get into google as well or any other company tbh ( my current tech job kinda blows ) ...
@suraj80922 жыл бұрын
Good luck!
@sanidhyax2 ай бұрын
This is so elegant. Have solved multiple of 2d array problems but never thought of accessing the rows literally by [bottom[[R] and [top][L]
@huimingli9207 Жыл бұрын
This is really a pure math problem. rotating a cell 90 degree, the index/coordinate change is from (x,y) -> (y, n-1-x).
@vaibhavkhanna29222 жыл бұрын
Great approach! Here you can see if you are confused with variable naming I have used some easy to understand names.Approach is still the same. void rotate(vector &matrix) { int size = matrix.size(); int startRow = 0; int startColumn = 0; int endRow = matrix.size() - 1; int endColumn = matrix.size() - 1; while (startRow < endRow && startColumn < endColumn) { int current_column_for_start_row = startColumn; int current_row_for_end_Column = startRow; int current_column_for_end_row = endColumn; int current_row_for_start_column = endRow; int current_size = endColumn - startColumn; for (int i = 0; i < current_size; i++) { int temp = matrix[startRow][current_column_for_start_row]; matrix[startRow][current_column_for_start_row] = matrix[current_row_for_start_column][startColumn]; matrix[current_row_for_start_column][startColumn] = matrix[endRow][current_column_for_end_row]; matrix[endRow][current_column_for_end_row] = matrix[current_row_for_end_Column][endColumn]; matrix[current_row_for_end_Column][endColumn] = temp; current_column_for_start_row++; current_row_for_end_Column++; current_column_for_end_row--; current_row_for_start_column--; } startRow++; startColumn++; endRow--; endColumn--; } }
@kwaminaessuahmensah89202 жыл бұрын
Mans went into god mode swapping the elements in reverse
@suhasdon13 жыл бұрын
Thank you. Best explanation without having to deal with 2 for loops with i, j or recursion and all other BS to be worried about.
@emanawel92242 жыл бұрын
This code makes the problem look way easier than it is! Love the code and explanation.
@ArunRampureАй бұрын
Have been struggling with coming up with an notion of using boundaries and using that i variable. Neet explanations for the neet code to write. Thanks for adding this.
@wij804410 ай бұрын
Easier solution for nXn matrix! Neetcode solution may be better suited for nXm matrix. function rotate(matrix: number[][]): void { const n = matrix.length; // Transpose the matrix, starting from i = 1 for (let i = 1; i < n; i++) { for (let j = i; j < n; j++) { [matrix[i][j], matrix[j][i]] = [matrix[j][i], matrix[i][j]]; } } // Reverse each row for (let i = 0; i < n; i++) { matrix[i].reverse(); } }
@anxonpues60182 ай бұрын
Good, explanation, improoving steps ... really golden pedagogical
@jananiadanurrammohan97952 жыл бұрын
Best explanation one could ever give for a problem!!!. Thank you for the effort and time you are putting into making all these videos.
@itspete24445 ай бұрын
"This is still a square if you tilt your head enough" - that got me laughing harder than it should have
@codewithtejesh12842 жыл бұрын
thanks a lot, great explanation! i stopped my leetcode subscription , now i am just watching your videos and solving question.
@annieonee2 жыл бұрын
This is the best explanation of this problem so I've found. Thank you so much for the content! Keep up the good work 👏
@mykytapiskarov72912 жыл бұрын
Amazing solution and explanaition! I spent about 2 hours trying to understand leetcode "Rotate group of 4" solution - but no luck. Here 15 minutes - and it's clear.
@sureshgarine2 жыл бұрын
I really like the way u handled minimizing the temp variable swap. very well explained. Thank you so much.
@ishaanjain4973 Жыл бұрын
I cant explain you how much this channel helps me !! Other channels just tell the transpose method which is not so intuitive, you always tell solutions which I can think in future in real interviews and exams. Thanks a lot Neetcode !! Keep up the good work man
@DanielTruongDev2 жыл бұрын
Great explanation, however if you recalled from Linear Algebra, this is basically transpose the matrix so (row,col) becomes (col,row). So here's a shorter solution in Python rows = len(matrix) matrix.reverse() #Reverse the matrix for r in range(rows): for c in range(r,rows): matrix[r][c], matrix[c][r] = matrix[c][r], matrix[r][c] #Transpose
@yabgdouglas6032 Жыл бұрын
my ego has made me attempt this problem almost 3 hours - thank you for this clean explanation!
@sumosam19803 жыл бұрын
Your videos are excellent. You do a great job of being super clear! I often come here to Neetcode to see if you have the solution as it is better than the official explanation. Keep up the great work!
@himanshubansal70402 жыл бұрын
This is a beautiful way to write the code for this tricky problem. Kudos!!
@nayanachandran70722 жыл бұрын
I must've have tried to understand this problem atleast 10 times and always failing to remember it. I now know I will never forget it! Thanks!
@josecarlosfontanesikling306 Жыл бұрын
It's possible to do this without any extra memory at all. Suppose you have variables x and y. You can swap them like this y=y+x x=y-x y=y-x This is all you need to transpose a matrix and to swap columns or rows. This rotation is just a transposition followed by inverting the order of the rows.
@pampanasubrahmanyam56932 жыл бұрын
small correction, in the for loop, at the range function it should be range(r) not range(r-1) for python3
@rohatgiy2 жыл бұрын
bro it’s an L
@Cruzylife2 жыл бұрын
wow this explanation was so clear and the code was so clean!!
@IncrementalNova3 жыл бұрын
Great content Bro :) Solution in Java: class Solution { public void rotate(int[][] matrix) { int n = matrix.length; int right=n-1, left=0; //neetcode solution video while(left
@sebastian_tec2 жыл бұрын
@theraplounge because as you enter in the inner loops the offset, or the amout that you have to add/subtract for the rotation decreases. in the video for the outer matrix the offset can be as much as 2, but in the inner matrix that offset is 0.
@inspiredomkar1239 Жыл бұрын
Thanks. I was looking for it.
@jimmycheong79702 жыл бұрын
This is a freaking amazing explanation. Thank you so much for sharing!
@KarthikChintalaOfficial2 ай бұрын
Like the approach. But it's tedious to really remember and do it. I like the transposing and reversing using a 2 ptr approach to do this.
@dollyvishwakarma22 жыл бұрын
No doubt I love your simple algos but this one can be done in a much simpler way which is to reverse the matrix row wise and then swapping the elements like we do for a transpose. Kudos to the great work you do :)
@user-xg2wj4dy5f Жыл бұрын
But to do that you will have to create another matrix which is the copy of the Matrix which is to be transposed and that is against the constraints of the question you have to work in the same Matrix
@dineshraj5957 Жыл бұрын
The best explanation by far of the layer rotation method. Damn it. The best!!
@krishnateja642810 ай бұрын
Cleanest explanation I have ever seen. Thank you!
@bruce7162 жыл бұрын
Thanks for the details and it is really easier to understand the concept with your good variable naming convention.
@chichiem2397 Жыл бұрын
These videos are great, this one in particular is perfect. I struggled with this a lot until I checked out this video. Awesome stuff!
@_majortom_2 жыл бұрын
You don't need 'top', 'bottom', 'left' and 'right' mambo jumbo! Simplified transformation for clockwise rotation of [ X, Y ] is: [ X, Y ] => [ Y, abs(X - len(matrix) - 1) ] ...and for counterclockwise: [ X, Y ] => [ abs(Y - len(matrix) - 1), X ] i.e. (switch coordinates and replace one with the absolute value of itself minus the length of the matrix minus 1) Do all transformations from [ 0, 0 ] using TEMP variable, then walk diagonally toward the center... [ 1, 1 ], [ 2, 2 ], ...
@_majortom_2 жыл бұрын
Just to point out: whenever you see a 2D, 3D or nD rotation or translation challenge, you know there is ONE rule that works for all the nodes. There are no special cases in rotation nor in translation. Always try to find the rule instead of breaking the matrix into small pieces -> i.e. more challenges.
@Kenny-st8cg Жыл бұрын
Since its python you can just do def rotate(self, matrix: List[List[int]]) -> None: n = len(matrix) l, r = 0, n - 1 while l < r: top, bottom = l, r for i in range(r - l): ( matrix[top + i][r], matrix[top][l + i], matrix[bottom - i][l], matrix[bottom][r - i] ) = ( matrix[top][l + i], matrix[bottom - i][l], matrix[bottom][r - i], matrix[top + i][r] ) r -= 1 l += 1 So theres no need for a temp variable, in that case we also wouldnt have to care about doing it in reverse. But I think readablitiy suffers a little
@brainmaxxing1 Жыл бұрын
An even better solution to consider: n = len(matrix) # Transpose Matrix for i in range(n): for j in range(i, n): matrix[i][j], matrix[j][i] = matrix[j][i], matrix[i][j] # Reverse Matrix for row in matrix: row.reverse()
@Kenny-st8cg Жыл бұрын
@@brainmaxxing1 Sure, but the TC of that solution is obviously much worse. For that solution theres no need for the second for loop either: n = len(matrix) for row in range(n): for col in range(row + 1, n): matrix[col][row], matrix[row][col] = matrix[row][col], matrix[col][row] matrix[row].reverse()
@brainmaxxing1 Жыл бұрын
The time complexity of both solutions is the same, O(n^2). You do more 'operations' but the performance is actually better in my testing (somehow because of how the computer handles the more common operations of reversing a row and transposing a matrix) My notebook testing all 3 colab.research.google.com/drive/1laaMa1XLalAsShcoqENbbD5peb-PdCHo#scrollTo=QSThsieXZiCO Also nice on removing the second loop, that does speed it up.
@Tensor082 жыл бұрын
I did this in one line 😎 which beats 97% matrix[:] = list(zip(*matrix[::-1]))
@ElijahGeorge2 жыл бұрын
This is a very intuitive explanation. Thanks so much!!
@Michael-zh3op2 ай бұрын
After playing around with matrices, this question was a cake walk.
@eltaylor778 Жыл бұрын
Great explanation, does anyone know why the range has to be range(right- left) instead of range(left,right)? The range(left,right) works on many of the smaller test cases but does not work on many of the harder ones. Help!
@kritmok187510 ай бұрын
that's because we always want to start the i with 0. let's take (2, 4) as an example range(2,4) return 2,3 but range(4-2) return 0, 1
@seungjunlee002 жыл бұрын
Thank you so much for the straightforward and clear answer!
@zekonja902 жыл бұрын
C# solution: public void Rotate(int[][] matrix) { int n = matrix.Length; for (int i = 0; i < n; i++) { for (int j = i; j < n; j++) { int tmp = matrix[i][j]; matrix[i][j] = matrix[j][i]; matrix[j][i] = tmp; } Array.Reverse(matrix[i]); } } Cheers!
@nayandhabarde3 жыл бұрын
Good work with comments and simplicity!
@bilalahmedkhan95182 жыл бұрын
I thought this was a very though problem but you made it so easy for me. Thank you!
@alinisar873 жыл бұрын
Beautiful solution, great explanation. Thank you so much.
@welcomb2 жыл бұрын
There a very easy way to do this. First transpose the matrix, which is just flipping along a diagonal in-place. Then reflect vertically, which is another simple in-place swap.
@Qxismylife2 жыл бұрын
I am thinking about the same. But the problem is we don't know if this is allowed, at least for the purpose of what this question is examining. If this is allowed then you can also use the 2D rotation matrix too.
@Qxismylife2 жыл бұрын
Just saw other comments. This is allowed. I am happy now.
@welcomb2 жыл бұрын
@@Qxismylife using a 2D rotation matrix may not be inplace as you need extra space for the matrix. Transpose and flip can both be done inplace
@mr.anonymous60982 жыл бұрын
Perfect Solution. When I first read the solution in the Cracking the coding interview book, I spent quite a lot of time and still could not understand it. You really simplified the logic which is so much easier to follow! Great Job, man
@yasharma23012 жыл бұрын
Knew the O(2*n^2) solution using transpose followed by inversion, thanks for this great one pass solution.
@nikiforovsansanich2 жыл бұрын
Perfect explanation! Thank you!
@bondinthepond2 жыл бұрын
Amazing approach - very structured! and of course backed by great visualization!! You've got a subscriber, just based on this!! :)
@Ilmard992 жыл бұрын
1) Invert the order of the rows 2) Transpose
@sunnybambooflute Жыл бұрын
Thanks for the clear explanation. I can understand it while I am in a food coma. lol
@leonfeng40062 жыл бұрын
please continue to make more videos, this channel is pure gold
@burburchacha9 ай бұрын
I hope you realise that you have a gift in explaining difficult concepts
@sanketkoli8641 Жыл бұрын
Very nice explanation. Thanks NeetCode!
@dr.merlot15322 жыл бұрын
The guys talking about transpose mean this: Geometrically, rotation of the plane by 90 degrees is equivalent to flipping about the diagonal line y=-x and then flipping about the y-axis. That's why this works.
@zekaiimran246422 күн бұрын
Best solution! thanks.
@rohitkumaram2 жыл бұрын
still your logic a more pythonic approach: class Solution: def rotate(self, matrix: List[List[int]]) -> None: l = 0 r = len(matrix) -1 while l
@shivaacharya72472 жыл бұрын
Great explanation! For some weird reason, for loop with range(l, r) does not pass all test cases!
@markvaldez5262 жыл бұрын
My code isn't passing either...
@shivaacharya72472 жыл бұрын
@@markvaldez526 range(l, r) doesn't work because we are iterating r - l times, not from l to r. For example, if l = 5, and r = 10, we need to run our for loop 5 times starting index from 0, 1, 2, 3, and 4 NOT from 5, 6, 7, 8, 9 which would be the case if we do range(5, 10).
@ugochukwustephenmbonu79742 жыл бұрын
@@shivaacharya7247 thanks for explaining. Cleared it up for me!
@pengmick2046 Жыл бұрын
Your explanation is so good
@suvrobanerjee2399 Жыл бұрын
Thanks for such a clear explanation.
@akshaibaruah17202 жыл бұрын
literally my go to channel..well was it really asked by microsoft?...I solved it by taking its transpose and then reversing it which is in place but needs two traversal
@ChocolateMilkCultLeader2 жыл бұрын
Your code was really elegant. Well done
@siddharthgupta61622 жыл бұрын
This video is so so so (X100) much better than the leetcode's solutions on this problem.
@navenkumarduraisamy62603 жыл бұрын
I really wish I had such clear approach
@reaiswaryaa2 жыл бұрын
Wow what an amazing explanation. Thank you !
@anooppatils2 жыл бұрын
Awesome Explanation. Just loved it. Keep up the good work :)
@FreeMayaTutorials3 жыл бұрын
Thanks for posting, this is great!
@johnlocke46952 жыл бұрын
There is no way I could have figured this out myself. Not even if they give me a million years time.
@akifozkan50652 жыл бұрын
made it look like so simple, great explanation
@ShivangiSingh-wc3gk2 жыл бұрын
Nice, explanation. I thought the same thing but got thrown off on how to get the indexes
@SarveshBhatnagar12142 жыл бұрын
I found more two approaches to this, First one is to reverse the image and then transpose the resulting matrix (Easier). Other approach is to do this matrix[:] = zip(*matrix[::-1]) I don't really understand what's happening here so if someone understands, please do tell :) Thanks!
@peterosi192 Жыл бұрын
Now this... I like!
@niteshsetin2 жыл бұрын
The explanation was awesome and helpful to understand the problem effectively. I was waiting to see the final input output but nevertheless the code is correct so i guess i will write and check myself 😁😊
@karthikjayaraman96463 жыл бұрын
Excellent article. Keep'em coming!
@jasonngan57473 жыл бұрын
This is super useful, thanks for the great work!
@harishsn48662 жыл бұрын
Thank you so much. You're the best.
@rahulsreedharan19222 жыл бұрын
Great video. Just one question - why are the elements replaced in a counterclockwise manner? What benefit does it have over the more intuitive way of just replacing it clockwise?
@nilkamalthakuria40303 жыл бұрын
Great explanation
@RandomShowerThoughts Жыл бұрын
very intuitive
@AshishSarin12 жыл бұрын
Thanks for this explanation. Really liked it.
@NeetCode2 жыл бұрын
Thank you so much!! Glad it was helpful!
@ashinshenoy842 жыл бұрын
Very well explained, but i spotted one line which could be shifted up. Line 10 can be put before the for loop isnt it ? no need to initialize it on every loop
@stith_pragya2 жыл бұрын
Thank You Brother for this amazing video.............🙏🙏🙏🙏🙏🙏
@aaronpuah9183 жыл бұрын
You really are the Bob Ross of LeetCode XD
@anandsrikumar007Ай бұрын
I took a temp array, copied all columns into the rows of the temp array but in reverse order, finally, I iterated the temp array and replaced matrix[row] = temp_array[row]
@algorithmimplementer4152 жыл бұрын
This is the best explanation!!
@KaushikChavali Жыл бұрын
I like the intuitively named variables.
@khatharrmalkavian33062 жыл бұрын
You know you can just swap instead of using a temporary. Walk through it: Swap TL with TR Swap TL with BR Swap TL with BL Shazam, the corners are rotated and aux space is O(0).
@trongthuong95812 жыл бұрын
How can u perform swap without temp variable xD
@khatharrmalkavian33062 жыл бұрын
@@trongthuong9581 There are two common methods and one other method that is CPU dependent: A) XOR swap: x ^= y y ^= x x ^= y B) Mathematical swap: x += y y = x - y x -= y C) x86 and x64 CPUs have the XCHG instruction, but it's likely to have the same performance as the other methods. Theoretically it would be faster since it can target a memory value directly, but doing so causes the CPU to lock all cores for synchronization, which is a massive performance hit. Operating just on registers, it has about 3 cycles of latency, which is similar to the XOR and mathematical methods.
@franly65610 ай бұрын
hi neetcode, i have a question, how to rotate matrix 45 degrees so the matrix size will increase, i trying to make the solution and now i want to give up (i have tried straight 5 hours btw). Can you make this solution a video pls.
@MinhNguyen-lz1pg2 жыл бұрын
Another great explanation my dude !
@eugenesol20744 ай бұрын
Nice, thanks for that
@collinskariuki25862 жыл бұрын
Hey. Thank you for the explanation. Query: In your drawing, you portray the bottom pointer moving up and the top pointer moving down, so it's kinda confusing for me because in your code you write 'bottom - i' and 'top + i'. Mind explaining this distinction?
@alexeymelezhik6473 Жыл бұрын
"top" and "bottom" variables are not necessary, one could replace them by "l" and "r"
@brainmaxxing1 Жыл бұрын
Sure, but why sacrifice readability? The difference is very small in terms of memory usage