Codeforces stream #2 - div1 A-B solving with explanation

Problem-solving of recent div1 A-B problems from Codeforces. Watch me if you want to practice Competitive Programming, algorithms or you want to learn for a coding interview. I share my thought process, explain everything, and mention similar problems that I know or techniques/algorithms that could be used too. Learn from me and grow your rating on Codeforces!
I'm known as Errichto. I compete in and organize programming competitions. I'm a finalist of ACM-ICPC, Topcoder Open, Facebook Hacker Cup and Google Code jam. I got a second place in Google Code Jam 2018.
What is Competitive Programming? en.wikipedia.org/wiki/Competi...
Follow me on Facebook: / errichto
Competitive Programming Discord: discordapp.com/invite/UzaURu7

[@filipposoldati1472]

2:29 Codeforces Round #517 - A: Cram Time 29:48 Codeforces Round #517 - B: Minimum path 1:30:30 Codeforces Round #124 - B: Infinite Maze 2:25:33 Technocup 2019 - Elimination Round 1 - E: Vasya and Good Sequences 3:31:56 Codeforces Round #272 (Div. 2) - D: Dreamoon and Sets Extra: 3:07:34 Improving suboptimal solution for 517B: Infinite Maze 3:26:47 Explanation for Educational Codeforces Round 3 - E: Minimum spanning tree for each edge

[@Errichto]

Thank you a lot!

[@shrad6611]

Please, guys, don't always compare him with tourist. He is best in his own way. Here he makes tutorial videos that help many people around the world. According to me he is best and I don't care about, he wins the competition or not but he is only one who helps us, tourist not.

[@nihalk3935]

👍

[@saikat93ify]

Appreciate your effort in making this video :)

[@Errichto]

Cool, I'm glad you liked it :)

[@arjuntomar215]

great gesture of helping others, it helps a lot please continue these streaming as much as possible ,like me lots of people will love to see your streams very very useful

[@SuperSam4y0u]

Thankyou so much Erichto! Your explanations were really helpful. I hope you keep making such videos and your channel keeps growing!

[@vicfred2989]

thanks for making this kind of videos, very appreciated

[@guttsman]

This is helping me a lot because this kind of problem almost always have simple and/or smart tricks involved. Thanks for the time invested and hardwork! =D

[@dopamineaddict9690]

thanks a lot. the video is great and very educational. please keep making as many of these as possible.

[@sanjaysingh5007]

sir please make more videos on this Type of contest problems of codeforces they teach us alot..your efforts are awesome ...and are helping the students very much...

[@rajavikramaditya6152]

I always thot D.E and F were very tough, but you actually made me believe that they are not. Thank you.

[@happyhappyguy5034]

F is very tough

[@user-du4pq7hh2x]

you are a genius! I wonder how that feels. Although I know not a stitch of what you do, I find it very interesting.

[@shrad6611]

Make more videos like this which have more explaination Love to watch your videos Big fan errichto

[@sanjaysingh5007]

sir please make more videos on the algorithms TOPICS and concepts and please tell us about the books our resources to boost our CP skills. Your videos are Great...

[@siddharthabiswas2147]

the videos are really good ,thank you

[@mizanurmazumder114]

Wow..! Its really a informative video

[@akhilbinani6246]

Codeforces Round #517 - B: Minimum path in the first part of the problem instead of DP, we can use Dijkstra`s algorithm to get the same matrix as of the DP matrix.

[@spamfriendly6489]

You are a god !

[@tylerf1902]

very intersting stuff

[@ankurdubey960]

It's really helpful for me. Though best results at 1.25x.

[@igorbeliyaveski7600]

WOW! Its cool maaaan

[@magnuswootton6181]

YOU GET TO READ MORE NOTES IF THE NOTES TAKE LESS TIME TO READ. but u read the same amount of words...

[@Haphazard1945]

I've been writing software for years and haven't interviewed in about 10. This is never used on the job so why is it tested for during interviews? Wouldn't system design make much more sense?

[@amhanafy]

why at 16:00 at least one set has (k*(k+1))/4 ?? and what is k ? the number of remaining numbers from right?

[@kamildebowski7003]

If you want to split A numbers into two groups, one group must have at least A/2 numbers. Here we have A=k*(k+1)/2. k is the number of remaining numbers on the left.

[@amhanafy]

ok now i know that if we want the remaining space between 2 sets k*(k+1)/4 but how we make sure that there's a space left so using the first while loop we make sure that the highest k here equal to i -1 can be splitted to 2 groups am i getting it right ?

[@kamildebowski7003]

You're getting it right. And the proof was explained in the video.

[@amhanafy]

@@kamildebowski7003 thanks kamil your work is really appreciated looking forward for new live streams greetings from Egypt

[@akaradet5387]

ดี

[@ahmedshawky9845]

for the first problem how could we prove that you need to select numbers from right to left instead of left to right?

[@Errichto]

I proved why taking from right to left worked. I also said some intuition why the opposite doesn't work: when you decide about some first numbers, you are left with big numbers that might not fit in either set/bag.

[@sandipsuryawanshi4788]

Good

[@imadudin2489]

is this cutoff ?

[@Errichto]

KZbin takes a few hours to process a stream, and then it's available in full length, including chat on the side.

[@imadudin2489]

okay, thank you. its full now

[@darknessgamerz7505]

nostalgia

[@devidengo]

Juluuiuuu 8:56 u