3 Sum | Brute - Better - Optimal with Codes

Problem Link: bit.ly/3X34JSI
Notes/C++/Java/Python codes:
We have solved the problem, and we have gone from brute force and ended with the most optimal solution. Every approach's code has been written in the video itself. Also, we have covered the algorithm with intuition.
Full Course: bit.ly/tufA2ZYt
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0:00 Introduction of Course
00:41 Problem Statement
02:56 Brute force approach (Using 3-pointer)
04:55 Pseudocode
07:36 Code
09:27 Complexity
10:26 Better approach (Using Hashing)
12:23 Dry run
18:09 Code
20:15 Complexity
22:20 Optimal approach (Using 2-pointer)
23:20 2-Pointer Technique
31:50 Code
36:41 Complexity

[@takeUforward]

Please do give us a like and subscribe, it won't cost you anything, but it will motivate me to make such kind of content more and more.

[@utsavseth6573]

Legendary stuff Raj bhai. Your explanation clearly shows you actually have a very strong depth on these fundamentals. And of course you do, you work for Google😉

[@deepak8720]

Awesome stuff. Liked and subscribed. Keep going. 👍

[@pardhi8959]

great content love u bhai

[@pardhi8959]

I start by like for all the video

[@Bhai9866]

Bhaiya code nhi chal raha hai 3 sum ki u give the condition sum is greater than 0 , less than 0 but didn't give the condition sum is equal to 0 why?

[@luckshaeey]

Tried 2 sum, 3 sum and 4 sum problems together as a beginner. It was so frustrating after a point before I understood the optimal approach 😂

[@rishav144]

true bro

[@it-51gulshanbhati89]

u r strong bro u have tried all as a beginner 😅

[@Akash-yr2if]

You have a lot more experience than the whole comment section combined.

[@user-ye4xi4py2k]

The optimal approach for 3sum is just the extension of optimal approach of 2 sum when the array given is sorted

[@joeljacob4685]

@@user-ye4xi4py2k yup !! you are right

[@shashankrajput8084]

That's what a explanation beginner require for these type of problems

[@mehulthuletiya497]

00:41 Problem Statement 02:56 Brute force approach (Using 3-pointer) 04:55 Pseudocode 07:36 Code 09:27 Complexity 10:26 Better approach (Using Hashing) 12:23 Dry run 18:09 Code 20:15 Complexity 22:20 Optimal approach (Using 2-pointer) 23:20 2-Pointer Technique 31:50 Code 36:41 Complexity

[@itzmartin20]

Just cameback for a quick revision, and now it's indeed got into my head, thanks for your crystal clear intuition!

[@Pamir026]

Yes! I was onto this optimal approach but my implementation failed because I wasn't thinking it through. Simply lovely explanation!

[@deepak8720]

Completely Understood your explanation! Thank you for what you are doing, and please continue the good work. You are an amazing teacher. Have watched 3 videos of yours and I was able to understand all 3 with out any confusions. Big thumbs up for the video. 👍

[@jeet-smokey]

We will never get such a detailed explanation of 3 Sum problem. You are a Legend for reason....Striver.....!!!!

[@subhranshuswayampravadash4656]

Thanks brother for helping and providing us amazing solutions of the most important questions that asked in MNC's. Thanks a lot brother🙏

[@PrashantSingh-qr3vn]

Are u a genius how do u know what doubts a newbie would have . U r just superb in explaining the Algo

[@cinime]

Understood! Super amazing explanation as always, thank you very much for your effort!!

[@abhijeetmishra3804]

how can one explain so smoothly man...Hats of STRIVER bhaiya

[@ruchikaahujaasm]

Explained all 3 approaches very clearly. Thank you so much!!!

[@pragyatripathi8833]

I love the way you teach bhayiya.❤❤ I don't have seen the teacher like you....you are God of DSA.

[@Manishgupta200]

Thanks for the in-depth explaination with in-depth time and space complexity

[@rajatyadav4077]

It's interesting-I initially tackled this problem with three nested loops, but when the time exceeded, I decided to find a way to eliminate one loop and ended up developing a two-pointer solution. Although I found the solution, I still enjoy watching Striver's videos to refresh my mind, spark creativity, and discover new approaches to problem-solving.

[@karthikeyan.s2565]

Bro 3 loops was the best I could think of, I can't able to optimize it How do you develop this logical thinking ? Could you help me with this ?

[@user-hp9kj8qt1h]

Me too pls

[@graviton001]

I also solved with two pointer approach on my own after 3 loops got time exceeded 😊 he built my logical thinking

[@rajatyadav4077]

@@karthikeyan.s2565 This is a long process bro, keep in mind the techniques you have already employed and then try to come up with ideas for how we may shorten the loop as much as possible. Actually, after successfully answering an easy issue, I usually attempt to answer it in three or four ways (if at all feasible). Occasionally, after solving the problem, I peruse other people's answers on Leetcode to discover new strategies, and the Striker video assisted me in approaching the problem.

[@ahssanakhtar5746]

Amazing content learn a lot every day from your course.Thanks for creating such an amazing course.

[@sharmavishal7239]

Bhai maine aapki dsa sheet aaj first time dekhi hai kya banayi hai bhai , sach main mja aa gya .... Thanku dil se striver bhai ❤

[@disciplines4]

nice all the three approaches, helped a lot.

[@RahulKumar-zp1ln]

THANK YOU FOR EXPLANING IN SIMPLE WAY

[@sdakshin1]

I found your explanation the best among all available... gd job

[@piyushroy3278]

Too good man, more and more kudos to you for such explanation. now im getting grip on building logic...finally.

[@swathigp3818]

Great examples, which helps understand the algorithm very clearly even for non CSE folks!!

[@welcometoc.s.easpirants]

Awesome explaination. Thank u for such a great content.

[@AmartyaPardeshi]

My man is doing God's work, thanks for this amazing playlist!

[@shubhamagarwal1434]

#Free Education For All.. # Bhishma Pitamah of DSA...You could have earned in lacs by putting it as paid couses on udamey or any other elaerning portals, but you decided to make it free...it requires a greate sacrifice and a feeling of giving back to community, there might be very few peope in world who does this...."विद्या का दान ही सर्वोत्तम दान होता है" Hats Off to you man, Salute from 10+ yrs exp guy from BLR, India.....

[@jingfulin2322]

Great job! your code is so clean.

[@S__Arslaan]

no need of condtion j

[@rohansingh6329]

awsm video striver ❤❤ the free education you are providing is helping a us alot.

[@user-bj9qx9yf1o]

Hi, you are doing extremely good work DSA topics. You making concepts very clear. Glad that I got your channel reference. But un luckily I am from JavaScript background , i am finding a resources like anything for DSA, I dint get any . Your help will be appreciated on this.

[@dipingrover1970]

amazing exlanation , loved this video

[@Bakwas_baate]

what a solution. MINDBLOWING!!!!

[@user-yz6yk4vt6q]

what a fantastic explantion!!!!

[@culeforever5408]

understood and came up with the optimal solution myself almost same. just used an extra set to store triplets 😅

[@sarangkumarsingh7901]

Another Awesome Lecture................

[@JackCoderr]

Thank you so much bhaiya....you are the best teacher ❤❤❤

[@newbie8051]

Was asked in Adobe interview for DEI hiring for specially abled candidates. Woah, thanks !

[@manvendrasingh4369]

While solving this problem, the very first approach which comes to my mind was optimal. Although the way I was handling duplicates was giving time limit exceeded error so I have to took help from gpt but rest of the logic was correct. Feeling extremely happy.

[@a1_32_aarushi8]

Thank you so much sir for such a nice explanation your are super sir❤

[@eashan2405]

Great explanation Striver ❤

[@gamingchampions4105]

gained a subscriber with your amazing explanation

[@rahulraaja5056]

Great Explanation 💯💯

[@joeljacob4685]

Beautiful dry run!! Understood😄

[@sayakghosh5104]

Awesome explanation....

[@NazeerBashaShaik]

Understood, thank you.

[@tanya8353]

Great Job again !!

[@priyanshuagrawal7509]

Now i can finally answer someone if someone ask me have you done 3Sum 😆. Thanks Striver 😉

[@guneeshvats46]

Amazing explanation

[@bopon4090]

Bro that hash map solution is so genius.

[@priyankaghosh2670]

best teacher in the world...........

[@arunprashanna7494]

Perfect explanation

[@samlinus836]

Thank you bro, love from Tamil Nadu ❤

[@anjigolla4853]

superb explanation brother👏

[@Azeem_Idrisi]

Amazing explanation 👌💯

[@udaytewary3809]

Understood bhaiya 🙏 ❤️

[@konankikeerthi]

Understood bro. Thank you

[@anasnadeem3259]

Great explanation 💯

[@Benstokes555]

mind blown, dopamine released, love u striver

[@dpxy1599]

got it nicely explained.

[@aditikaushik3073]

Thanks a lot, sir !!

[@AbhishekKumar-nz9dn]

understood brilliantly 😘

[@tarunsingh7826]

Best explanation 🔥

[@bitran4283]

love it, thanks

[@parthtiwari8152]

understood thanks striver

[@AniketKumar-hf2bo]

understood ,thnx for explanation ❤❤❤❤❤❤👌👌💕💕💕💕

[@user-xv7ms8bn2b]

best explaination !!!

[@shashankgsharma0901]

we can keep the indexes of the elements in the hashmap as well, in one loop; then while taking i and j, we can check whether the index is same as that of i or j or not. That would require less time complexity than the better solution.

[@user-if3ce9gm7p]

Understood sir thank you soo much sir

[@sayantanpoddar5428]

understood!!! please came up with string series...please

[@harshilpatel3205]

Understood 🙏🏻

[@souravmehraniya2832]

Keep going brother ❤

[@hashcodez757]

Mza aagya Understood!!

[@sahulraj9536]

we can do a small improvement int the optimal code if nums[i]>0 then we can break the loop and return answer directly

[@nightgamer8953]

HashSet in C# still stores duplicate List in C# . Is there any alternatives in C# to store unique List of Integers?

[@Sumeet_100]

Thank you ❤

[@sakshiagrawal9106]

thank you so much bhaiya❤

[@swacharahman5084]

Thank you bhaiya, Love from bangladesh

[@saketjaiswal9381]

thank us sir again

[@SatheeshKumar-kg1yn]

Clealy understood

[@UECAshutoshKumar]

Understood 👍

[@anmjubaer]

Great explanation but what about the time complexity of those 2 while loops from the optimal solution? Can you elaborate a bit here please?

[@_SahilShah]

Understood! I went somewhere near the optimal approach but wasnt able to come up with the concrete solution

[@GhostVaibhav]

Understood🔥

[@RituSingh-ne1mk]

Understood!

[@manambalaji9547]

Excellent 👌

[@Shivi32590]

thank you

[@anuragprasad6116]

3-sum code using 2 for loops and 1 while loop. Using for loops helps in more readability in this problem. // Sort the vector and create ans array. sort(arr.begin(), arr.end()); vector ans; // Iterate the sorted array. for (int i = 0; i < n; i++) { // Make sure first element of triplet is unique. // Now whole array on right of 'i' is a 2-sum problem. if (i > 0 && arr[i] == arr[i-1]) continue; // Take -ith element as target. int twosum = -arr[i]; int right = n-1; // Look for unique 2nd element in the search space. Notice that for // each unique i, the pairs that create 3sum with it are unique. // Similarily, for each unique j, the 3rd element will be unique. for (int j = i+1; j < right; j++) { // Looking only for unique 2nd element. if (j > i+1 && arr[j] == arr[j-1]) continue; // Look for its partner. while (j < right && arr[j] + arr[right] > twosum) right--; // No need to skip. All the 2nd elements are unique! if (arr[j] + arr[right] == twosum && j != right) ans.push_back({arr[i], arr[j], arr[right]}); } } return ans; Similarily, 4sum can be broken down as: first unique element + 3sum in remaining search space.

[@shubhamkumar170]

Understood!! ❤❤

[@vishalgupta7522]

Line 29: Char 10: error: type 'vector' does not provide a call operator ans(st.begin(), st.end()); ^~~ 1 error generated. brute force code

[@lakshmiprasanna7058]

Understood 💯💯💯

[@trinitykhuman]

I was looking for brute force approach tried myself but couldn't remember I have to used set DS but now , I can understand where I was wrong. Thanks for the tutorial.

[@impalash_ag]

Hi Raj, there are 2 slight mistakes in your optimal solution. 1: The for loop will run till n-2 instead of n, because when i=n-1, j becomes n (j=i+1=n-1+1) and num[j] throws out of bound exception. 2: We could also insert another check in the for loop(nums[i] = 1 there's no way any 3 elements sum would be 0 since the array is now sorted. 3: Here's the more readable code(JAVA): class Solution { public List threeSum(int[] nums) { int n = nums.length; List result = new ArrayList(); Arrays.sort(nums); for(int i=0; i low && nums[high] == nums[high+1]) high--; } else { result.add(Arrays.asList(nums[i], nums[low], nums[high])); low++; high--; while(low < high && nums[low] == nums[low-1]) low++; while(high > low && nums[high] == nums[high+1]) high--; } } } }

[@firebout7675]

understoood

[@arnavumarkar8259]

Thank You

[@placement123]

when implementing the second approach instead of using set, we can use unordered_map(with the second key as its index), and we will start i from 0 and j from i+1 and for the third value we can ensure by checking that the index of the last target element from the map should be greater than j :)

[@lakshsinghania]

hey, im not able to digest this thing in the 2nd approach arr is -1 0 1 2 -1 4 and the i & j are pointing at -1 and -1 so arr[k] = -(-2) = 2 so for this we need to search in the entire array right and he stored [0 1 2] elements between -1 and -1 but what if the arr was like this 1 0 1 2 3 -4 and i is pointing to 1 and j pointing to 3 then arr[k] = -(4) = -4 then if we store [ 0 1 2 ] we will not find in the set as -4 is after the j pointer could u pls make me understand this as im bit confused

[@CoDeEnthusiast-ev9zu]

​@@lakshsinghaniayou are right but there is a catch here , When i is pointing to 1 and j is pointing to 3 we need to search for -4 in the hashset which is not available. However after that we will add the arr[j] into the hash set i.e. we will add the element 3 into hash set .. So in the next step j will point to 4 now we have to search for -(1-4) = 3 and this element 3 is present in the hashset thereby we will get the required unique triplet

[@YourCodeVerse]

Understood✅🔥🔥

[@senseiAree]

Understood ❤

[@her_soulmate]

Understood 🎉

[@abhishekverma9946]

Understood.🙂

[@VishalPanwar-df5ek]

Understood man !!!!!!!!!!!!!!!!!!