HackerRank 2D Array - DS Explained - Java

[@hcadethc]

That's what I am talking about Nick, I love what you said about keeping going until you get to Google, I am trying man, these easy problems are not so easy or straight forward, but I am learning. Thanks a lot.

[@anth7rax]

did you get to Google?

[@ruthless5274]

What about now?

[@RicoRaiden-s3c]

How about now?

[@chaosavenger2]

For those following along in javascript, Number.MIN_VALUE is the smalled positive, non-zero number that can be represented in javascript so you would use negative max value (-Number.MAX_VALUE)

[@musicjunkie421]

That was nice dude. I always ignored the constraints section before watching this video.

[@opalski5417]

Thanks a lot for your explanation Nick, its easy to understand than i'm searching in google.

[@snehangshuchakraborty1458]

Thank you so much Nick!! You just made it so simple!!

[@TDavisOfficial]

I'm just starting these challenges. I am a total newbie. But wouldn't one way to make it a little more efficient be to set the loop to return automatically if the sum is 63? That way if your input's first hourglass is seven nines you don't continue checking.

[@suyashrahatekar4964]

You explained it with so ease.

[@perihanhill4397]

Thanks for explaining with easy steps! Done.

[@mohammadyahya78]

Hello Nick. Thank you for the videos. Please upload more Hackerrank videos.

[@WarReDeeMeR]

How do you set up HackerRank to be in arrays not Lists in the editor.

[@tahalaalaoui7809]

Same problem

[@aronhidvegi3174]

Why don't loop it through 4 times and you don't need length int for the rows and columns?

[@saifa.3950]

This would be O(n^2) correct? since youre nesting for loops. Is there a better way to do it where we can get a more optimal run time? I feel like in an interview itd look great if we could explain this this solution as the brute force solution then say theres a better one. But I could only think of this way.

[@zzzz26526]

I'm still not sure about the full solution but I think you can iterate over the 2d array in just 1 loop. Since you already know where the values you're looking for are in respect to the current index you can just use a formula to access the next row without having to use another loop. I'll get back to you about the solution but I was also wondering about the optimization for this.

[@sahandevaka9906]

public static int hourglassSumO(List arr) { int result = 0; if(arr == null || arr.size() == 0){ return result; } int rows = arr.size(); int columns = 0; int count = 0; int totalMax = -9*7; for(int i = 0; i < rows - 2; i++){ count++; int max = arr.get(i).get(columns) + arr.get(i).get(columns+1) + arr.get(i).get(columns+2) + arr.get(i+1).get(columns+1) + arr.get(i+2).get(columns) + arr.get(i+2).get(columns+1) + arr.get(i+2).get(columns+2); totalMax = Math.max(totalMax, max); if(count == rows - 2){ count = 0; i = -1; columns++; } if(columns >= rows - 2){ break; } } result = totalMax; return result; }

[@lancedolan]

@Saif It depends how you define `n`. If `n` is your number of rows (and also columns), then yes it would be O(n^2), or O(rows * columns). HOWEVER, we're not interested in knowing the time complexity with respect to rows and columns, we're interested in the time complexity with respect to the actual data set. The rows & columns are an arbitrary artifact of the fact that we're representing the data in 2 dimensions here, so it's irrelevant. If `n` is the number of elements in the total dataset, then that nested for loop is actually a way to make 1 pass over the n elements, and is thus O(n).

[@Rytuvidu]

Oh my god! What an eye opener

[@anirbansarkar6306]

wow, that min_val setting logic was awesome.🤐

[@hinata01mcr]

Thank you for teaching us the solution!! Subscribed!

[@hankim394]

same

[@Matee2334]

How to solve this, if the method takes List arr as parameter and not a two-dimension array?

[@sahandevaka9906]

public static int hourglassSum(List arr) { int result = 0; int rows = arr.size(); int columns = arr.get(0).size(); int totalMax = -9*7; for(int i = 0; i < rows - 2; i++){ for(int j = 0; j < columns - 2; j++){ int max = arr.get(i).get(j) + arr.get(i).get(j+1) + arr.get(i).get(j+2) + arr.get(i+1).get(j+1) + arr.get(i+2).get(j) + arr.get(i+2).get(j+1) + arr.get(i+2).get(j+2); totalMax = Math.max(totalMax, max); } } return result; }

[@gabrielahernandez4236]

Super helpful, thanks!!

[@viveksagar33333]

Thanks for the explanation.

[@shadabhasankhan1518]

Damn ! That was really a good explanation. Thanks

[@mattturner1718]

Great explanation bro

[@shokai036]

Very elaborating!

[@pavandeshpande7805]

Thanks. Good explanation.

[@Salesforce_Nexus]

Can you tell we why you have taken int column=arr[0].lenght instead of arr.lenght . i'll be glad if you can tell the difference.

[@rucha3385]

public static void main(String[] args) { int[][] foo = new int[][] { new int[] { 1, 2, 3 }, new int[] { 1, 2, 3, 4}, }; System.out.println(foo.length); //2 // gives count of rows System.out.println(foo[0].length); //3 // gives count of columns for particular row System.out.println(foo[1].length); //4 } for rows foo.length directly,but in case of 2 d columns can change so foo[0].length for columns.

[@Salesforce_Nexus]

@@rucha3385 thanks

[@nikitarai_cse8748]

DS Stands for Data Structure Nick

[@yosuasimanjuntak2822]

Thanks nick ! Very appreciate

[@navinchainani4721]

So that beginners should understand

[@sreedhar2847]

DS - DATA STRUCTURE

[@NickWhite]

lmao

[@rahulsingh-lv5xp]

every @@NickWhite indian know the full forms of ds

[@shivamkumar-qs7er]

Amazing as per standards...!

[@kaiserkonok]

DS stands for data structures and algorithm

[@abdullahAboelkhair]

BRO U ARE THE BEST

[@jordanaugust1207]

DS stands for data structure, my dude

[@DamienPictures]

Thanks, dude.

[@pathup3975]

IT WORKS WITHLIST IN HACKERANK

[@yungkazi7629]

Hey Nick, new subscriber here, I was just a bit confused on why you subtracted -2 on the rows and columns, is there any link I can check out to do some reading on that end, I get the rest it's just the -2 that's really throwing me off, appreciate it.

[@MrACrazyHobo]

There is an arr[i][j+2] in the code. If he doesn't subtract 2 from the rows and columns, then assuming rows = 5 and columns = 5 he will have arr[5][7]. The 7 is out of bounds, which is where the indexoutofbounds exception occurs

[@codeunited5905]

I think DS stands for 'Data structures'.

[@ShivamKumar-sc1zx]

Hi Nick, Can you help me solve a 2D array question!

[@rahulsingh-lv5xp]

DS stand for datastructure

[@tinderizer3397]

I tried doing EXACTLY what you did, and kept getting compilation errors.

[@zenshyam]

Hello..Did your code works after you tried his solution?

[@penguimTwo]

I got Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 6 at Solution.hourglassSum(Solution.java:20) after copying exactly

[@mattmaliaros6236]

Post your code here if need be but he did mention this issue around 5:40 -- The issue is an Index Out of Bounds Exception You need to change your for loops to subtract 2 from your conditional statement. For(int i = 0; i < rows -2; i++) and For(int i = 0; i < columns-2; i++)

[@azims602]

nick can you make your video full screen it is buriq 8 bit

[@shreeyabhosale1456]

Thanks Your are asome

[@Darktruth1122]

Awesome!

[@navinchainani4721]

I urge you make video like a beginner

[@Nakapeesh]

nice

[@RandomNoob1124]

Subscribed

[@chiragcode4721]

i think you need to learn to explain things properly. This video was an epitome of learned code & that's vividly not the way to code. Thanks

[@shivamkumar-qs7er]

Amazing as per standards...!