Winning LeetCode Weekly Contest 174 + Explanations

My first win on LeetCode! Anyways, explanations start at 14:05. If they are a bit unclear, feel free to ask questions in the comments below so that I can improve!
Bonus: I challenge everyone to solve the last problem in O(n), as opposed to the O(n^2) solutions most people had. Comment your solution in the description!
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[@rogernadal9106]

Amazing, Congratulation William! You can save more time by running multiple tests in one go. You just have to paste the i'th test after (i-1)th test in the custom test section. Give it a try and it may save you couple more mins.

[@tmwilliamlin168]

Wow, thanks! I never knew about that.

[@premierdota9128]

Congrats William! I wish I couldve done the third and fourth problem too. Will keep trying!

[@bensonyuan5083]

dude this is awesome! Looking forward to this weekly~

[@bharathateja2797]

Excellent . I was using topological sort to find longest path in DAG . Now i learnt 2nd method using simple dfs by watching your video . Thank u so much.

[@rohithgupta9672]

Thanks lin

[@saikat93ify]

Congratulations on Winning your first LeetCode Contest, William ! Although this surprises me as I thought you had already won many. May you win many more in the future and May God Bless You. May I ask a question for C ? Here was my approach - We want to maximise (S1.S2) where S1 + S2 = S, the sum is invariant. Now, if the sum of S1 and S2 is invariant. The largest sum is when |S1 - S2| is as small as possible. I tried each edge and examined the difference between S1 and S2 and took the values where |S1 - S2| is the minimum possible. I thought taking the products directly would overflow and if we take the products mod M = 10^9 + 7, it might not be accurate. For example 10^9 + 9 > 5 but 10^9 + 9 (Mod M) < 5 (Mod M) Can you please explain how you avoided overflow ?

[@tmwilliamlin168]

I used long longs and only took the answer modulo M when returning the final answer.

[@saikat93ify]

William Lin Will the product always fit in 64 bits ?

[@tmwilliamlin168]

Yes, according to the constraints, S1+S2

[@saikat93ify]

@@tmwilliamlin168 Thanks !

[@bhaskarbhasku2921]

does make_pair have more complexity than array stl?

[@tmwilliamlin168]

They both work in constant time (if you mean time complexity). I'm not sure which one is faster, but they are both fast enough that it will not matter in most cases. I use array because, for example, you can make triples easily by writing array.

[@bhaskarbhasku2921]

:)

[@codeWithBatta]

Sir if you only make vedios of questions you solve only explaining ... It will be of great help. :)

[@codeWithBatta]

Like you just explain the code of what you have done in questions of recent educational round at codeforces .. you can open your code and explain your logic .. about 1-3 minutes per question maybe

[@tmwilliamlin168]

I plan to give explanations for cf educational rounds as well, but just after I finish solving all of the problems.

[@AlexWice]

Nice screencast and congrats on 1st. Would you like to join the coding interview community at interview.solutions/ ? There's a decent audience to showcase your explanations there.