Hello Codeforces Community, I am glad to share HackerRank World Codesprint 11 starting on 26th May 2017. The contest duration is 24 * 2 =48 hours.

The winners of the contest will win up to 2000USD cash prizes. Also, there are opportunities to win T-shirts and Amazon Gift cards.

The contest will be rated. If two person gets the same score, the person who reached the score first will be ranked higher. There will be 7 algorithmic challenges in the contest including an approximate challenge.

The problems are prepared by svanidz1, tunyash, CMaster, muratt and Shafaet. Thanks to Wild_Hamster for testing the challenges and finalizing everything.

Update: Contest is starting in 10 minutes.

Update: The contest ended, congrats to the winners.

Happy Coding!

Hello Codeforces Community,

I would like to invite you to HackerRank's RookieRank-3 contest. The contest will start on 5th May 16:00 UTC.

The contest is specially targeted towards newcomers who recently started competitive programming and looking forward to improving their skills. The contest duration is 48 hours and there will be 5 algorithmic challenges.

Top 3 coders ranked on the leaderboard win a Champion T-Shirt. We will also reward 10 coders picked at random from the top 200 on the leaderboard with a Champion T-Shirt. You must be a rookie to be eligible to win a T-Shirt

I hope you will enjoy the round!

Hello Codeforces Community, I am glad to share HackerRank World Codesprint 10 starting on 28th April 2017. The contest duration is 24 * 2 =48 hours.

The winners of the contest will win up to 2000USD cash prizes. Also, there are opportunities to win T-shirts and Amazon Gift cards.

The contest will be rated. If two person gets the same score, the person who reached the score first will be ranked higher. There will be 7 algorithmic challenges in the contest.

The problems are prepared by malcolm, svanidz1, sgtlaugh, nabila_ahmed, kevinsogo and Shafaet. Thanks to danilka.pro , Wild_Hamster, HellKitsune and allllekssssa for testing the challenges and finalizing everything.

Update: the contest is starting in an hour!

Happy Coding!

I invite you to take part in HackerRank HourRank 19 starting on April 2nd 2017. The contest duration is 1 hours. There will be three algorithmic problems of various difficulty.

The chief author of this round is torquecode. The chief tester is pkacprzak. Thanks to Piotr Gajowiak and Wild_Hamster for pre-solving the problems and giving valuable opinions.

The problems will have subtasks to make them interesting for everyone. I strongly recommend to read all the problems.

The contestants are ranked by score. If two contestants get the same score, the person who reached the score first is ranked higher.

Happy Coding!

Hello Codeforces Community, I am glad to share HackerRank University Codesprint 2 starting on 17th February 2016. The contest duration is 24 * 2 = 48 hours.

The winners of the contest will win up to 2000USD cash prizes. Also, there are opportunities to win T-shirts and Amazon Gift cards. (Winners will be required to give proof that they are currently enrolled in the university they represented during University CodeSprint.)

The contest will be rated. If two person gets the same score, the person who reached the score first will be ranked higher. There will be a separate ranklists for schools.

There will be 8 algorithmic challenges in this contest. Many of the problems will have smaller subtasks, so I highly recommend you to read all the problems.

The problems are prepared by tunyash, allllekssssa, osmanorhan, DmitriyH, darkshadows, bertho_coder and me. Thanks to wanbo, adamant, danilka.pro, svanidz1, zemen for helping them with testing. Special thanks goes to Wild_Hamster for helping to finalize everything and to allllekssssa for finding mistakes in the statements.

Update: Contest is starting in less than two hours!

Update: The contest has ended, the editorials are now available. Congrats to tourist for solving everything in just 143 mins!

Editorials will be live soon after the contest ends.

Hello Codeforces Community, I am glad to share HackerRank World Codesprint 9 starting on 27th January 2017. The contest duration is 24 * 2 =48 hours.

The winners of the contest will win up to 2000USD cash prizes. Also, there are opportunities to win T-shirts and Amazon Gift cards.

The contest will be rated. If two person gets the same score, the person who reached the score first will be ranked higher.

There will be 7 normal algorithmic challenges and 1 approximate challenge in this contest. I highly recommend you to read all the problems. Most of the problems contain cool figures and subtasks!

The problems are prepared by zemen, Wild_Hamster, kevinsogo, allllekssssa, forthright48, nabila_ahmed and bishop15. Thanks to danilka.pro, niyaznigmatul and wanbo for helping to test the problems. And again special thanks to Wild_Hamster for helping to finalize everything.

(By the way, danilka.pro is now known as danilka.pro!)

Update: Contest is starting in less than 5 minutes.

Update: The contest ended. We will soon announce the winners. Meanwhile, let us know if you liked or didn't like the problem-set.

Happy Coding!

Start your new year with Hourrank 16 on 2nd January, 2017. You have just 1 hour to solve 3 algorithmic problems.

The chief author of the round is svanidz1. Thanks to danilka.pro, malcolm for testing. And finally thanks to Wild_Hamster for helping to finalize the problems and dataset.

If two person has the same score, the one who reached the score first will win. There are subtasks in some of the problems, so I highly recommend you to read all the problems.

I wish you high ratings in the new year!

Update: The contest is starting in 5 mins.

Scoring: 15-25-60-70

The contest has ended, congrats to the winners:

The editorials are live, ratings are being updated.

Please wait for 6-8 weeks for the prizes.

Happy Coding!

Hello Codeforces Community, I am glad to share HackerRank World Codesprint 8 starting on 17th December 2016. The contest duration is 24 * 2 =48 hours.

The winners of the contest will win up to 2000USD cash prizes. Also, there are opportunities to win T-shirts and Amazon Gift cards.

The contest will be rated. If two person gets the same score, the person who reached the score first will be ranked higher.

There will be 7 normal algorithmic challenges and 1 approximate challenge in this contest. I highly recommend you to read all the problems. Most of the problems contain cool figures :).

The problems are prepared by svanidz1, malcolm, darkshadows, kevinsogo, robinyu, torquecode and me.

I would like to give special thanks to Wild_Hamster who worked really hard to finalize the problems and testing the data. Also thanks to wanbo as always for testing.

Update: Score of the problems are 10-20-30-50-60-75-85-100. The last problem will have binary scoring.

Update: The contest has ended, editorials are now available. Congrats to the winners!

Ratings will be updated soon. Don't forget to give your feedback!

Happy Coding!

Hello Codeforces Community, I am glad to share HackerRank University Codesprint starting on 10th November 2016. The contest duration is 24 * 3 =72 hours.

The winners of the contest will win up to 2000USD cash prizes. Also, there is opportunity to win T-shirts and Amazon Gift cards. (Winners will be required to give proof that they are currently enrolled in the university they represented during University CodeSprint.)

The contest will be rated. If two person gets the same score, the person who reached the score first will be ranked higher. There will be a separate ranklist for schools.

There will be 7 normal algorithmic challenges and 1 approximate challenge in this contest. Many of the problems will have smaller subtasks, so I highly recommend you to read all the problems.

The problems are prepared by svanidz1, malcolm, ma5termind, nabila_ahmed, allllekssssa, forthright48 and Mehdi. Thanks to wanbo, danilka.pro, tunyash for testing the challenges.

Scores of the problems:

• 5 [70% score for the 1st subtask]
• 15 [50% score in the subtask]
• 30 [30% score in the subtask]
• 50 [25% and 50% score in two subtasks]
• 70 [Approximate problem]
• 80 [40% and 70% score in two subtasks]
• 80 [20% and 50% score in two subtasks]
• 100 [Binary score, must pass all the test cases to get positive score]

Editorials will be live soon after the contest ends.

Another HourRank round is on the way! The time is 4th October 2016, 16:30 UTC. You have just 1 hour to solve 3 algorithmic problems.

The authors for this round are ma5termind, scorpion and me. wanbo tested the problems. tunyash and allllekssssa helped a lot to finalize the selection.

We tried our best to make the round interesting. All the problems have short statements. There are subtasks in each of the problems, so I highly recommend you to read all the problems.

Scores of the problems:

• 25 [70% score for the 1st subtask]
• 50 [30% score for the 1st subtask and 60% score in the 2nd subtask]
• 60 [25% score for the 1st subtask and 70% score in the 2nd subtask]

If two person has the same score, the one who reached the score first will win.

Update

The contest has ended and rating updated. Let us know your feedbacks!

Top-10 winners will get a cool HackerRank t-shirt.

Hello CodeForces Community!

I am glad to share that HackerRank's World Codesprint 7 is scheduled on 24-September-2016 at 16:00 UTC. Contest duration is 48 hours.

The contest is sponsored by Cardlytics, Ready-talk, Indeed Prime, NCR, Coursera and Sonoma. Contest site will be continually updated to reflect upcoming sponsors.

The problems were prepared by zemen, malcolm, muratt, svanidz1, forthright48, nabila_ahmed and Shafaet. Thanks to wanbo, danilka.pro, ikbal, allllekssssa and niyaznigmatul for testing/pre-solving the problems.

The contest will be rated. If two person gets same score, the person who reached the score first will be ranked higher.

Update: The contest has ended, the editorials are available now. We will announce the winners and update the ratings soon. Meanwhile, let's discuss about the problems!

Update

Only two guys got full score in this contest in 48 hours, they are:

• uwi
• zimpha

3 guys got 390 out of 400:

• biGinNer
• Patrick Smith
• Miguel Raggi

This suggests that the problem-set was very hard. Apart from the coders in top two, there are two other coders ("Ayman Eltemsahi" and "Ivan Livinsky") who solved the last problem but they are not in top-10.

See you next time!

Happy coding!

Hello everyone!

I am glad to invite you to the 11th edition of HourRank. The contest starts on August 2nd 16:30 UTC (View local time).

HourRank is a super short one hour long algorithmic contest. This time we will have 3 challenges, created by me, harshil and forthright48. As always, thanks to wanbo for testing the challenges and thanks to pkacprzak for helping with editorials.

There are subtasks in each of the problems, so I strongly encourage you to read all the problems.

Participants are ranked by score. If two participants have the same score, the one who reached the score first, wins.

Top-10 contestants will get a HackerRank Tshirt.

In the last round no one was able to get perfect score (though all the problems were solved). Let's see what happens in this round!

Update: scoring 30-50-75

The contest ended. The editorials are now open. Congrats to the winners:

anta

Zlobober

el_sanchez

yosupo

I_love_Tanya_Romanova

Only top 4 got the perfect score. Congrats to all.

I hope you liked the round, please share your feedbacks.

Happy Coding!

Hello CodeForces Community!

I am glad to share that HackerRank's World Codesprint #4 is scheduled on 23-July-2016 at 4pm UTC. Contest duration is 24 hours.

You can win up to $2000 Amazon gift cards/bitcoins, medals and t-shirts. [Note: Winners from US and India will receive Amazon Gift Cards. Winners from other countries will receive equivalent USD amount in bitcoins.]

The problems were prepared by zemen, ma5termind, forthright48, allllekssssa, tunyash, shaka_shadows, and nabila_ahmed. Thanks to wanbo, malcolm for testing and pre-solving the challenges. Special thanks goes to allllekssssa who helped a lot to prepare the problem-set.

The contest will be rated. If two person gets the same score, the person who reached the score first will be ranked higher.

Update: Scoring 15-25-40-50-60-75-75-90

Update: The contest has ended, congratulation to the winners:

uwi

xyz111

FatalEagle

izban

anta

Xellos

ecnerwala

Al.Cash

negativebplusorminus

nfssdq

Update: We regenerated the leader-board as the updated score wasn't reflecting after rejudge. There is a slight change in top 10 as ecnerwala moved up, but luckily the set of people didn't change.

Let us your opinion about the contest!

Happy Coding!

Welcome to the 10th edition of HackerRank HourRank! It's an hour long contest with 3/4 algorithmic problems. The event will take place on 6th July 04:30UTC, see the exact time here.

The chief author of this round is kevinsogo and the chief tester is wanbo.

The contest will be rated. If two person gets same score, the person who reached the score first will be ranked higher.

The top 10 will get awesome HackerRank t-shirts. Editorials will be available at the end.

Happy Coding!

Edit: The time was wrong in the post, updated now. Note that the contest is starting in an unusual time.

Update: Score of the problems are 25-40-60-80

Contest has ended, congrats to the winners:

JoeyWheeler

anta

jiry_2

Nobody could solve all the problems. The only contestant to solve the 4th problem is y0105w49 (but ended up in 9th position).

Hello CodeForces Community!

I am glad to share that HackerRank's World Codesprint #4 is scheduled on 25-June-2016 at 9am PST / 4pm UTC / 9:30pm IST UTC. Contest duration is 24 hours.

You can win up to $2000 Amazon gift cards/bitcoins, medals and t-shirts. [Note: Winners from US and India will receive Amazon Gift Cards. Winners from other countries will receive equivalent USD amount in bitcoins.]

The contest is sponsored by Monsanto, Indeed Prime, Memiah, Argos, Level(3), Rocketfuel and Cloud Academy

The problems were prepared by zemen, svanidz1, fedimser, sgtlaugh, nabila_ahmed, and myself. Thanks to niyaznigmatul, ikbal, danilka.pro, adamant and muratt for testing and pre-solving the challenges. Except couple of problems, the statements are really short :).

The contest will be rated. If two person gets the same score, the person who reached the score first will be ranked higher.

Score of the problems are: 15-25-50-60-80-90-100

Update: The contest has ended. Congratulation to the winners:

xyz111

Shik

Egor

simonlindholm

Stilwell

Happy Coding!

Hello CodeForces Community!

HackerRank is back with another World Codesprint! Join us on 21st May, exact time can be found here.

Its your chance to win upto $2000 Amazon gift cards/bitcoins and tshirts. [Note: Winners from US and India will receive Amazon Gift Cards. Winners from other countries will receive equivalent USD amount in bitcoins.].

Contest duration is 24 hours. The contest will be rated. If two person gets same score, the person who reached the score first will be ranked higher.

The challenges were prepared by osmanorhan, muratt, ma5termind, forthright48, CherryTree. I would like to thank wanbo and malcolm for helping to prepare this round.

Editorials will be live soon after the contest ends, I invite everyone from experts to beginners to participate and solve challenges. I hope everyone will enjoy the contest.

Update: The contest is in 2 hours.

Score Distribution: 15-25-40-50-60-70-80-100

Edit: Rating updated!

Winners:

jqdai0815

FatalEagle

izban

I_love_Tanya_Romanova

Al.Cash

Hi Codeforces Community,

HackerRank is going to arrange a game theory educational contest on May 13th.

The contest will be 5 days long. In each day we will release 2-4 problems. The first day will contain adhoc games, the second day will contain Nim games, the third day will contain Grundy games and last two days will contain some interesting games involving DP, greedy and Mathematics.

The problem-setters for this round are allllekssssa, forthright48 and me. Thanks to wanbo for helping to prepare the round.

The contest will be interesting to anyone who just started learning Game Theory. Last two days will contain interesting problems for everyone.

Top 10 in the leader-board will get a t-shirt.

Hope everyone will enjoy the contest!

Happy coding.

Update: The contest is starting in less than an hour.

Update: The contest has ended. I hope you learned something new from this contest. The editorials are now available. Please share your opinion in comments.

Let's learn about Staircase Nim by solving move the coins problem that appeared in HackerRank April World Codesprint. Among the problems I have ever created, its one of my favorites. If you don't want to solve that problem but want to learn about staircase-nim, just read the first part of this blog.

Let's start with some backgrounds.

Staircase Nim

This problem is a variation of Staircase Nim problem, which is a not-very-well-known variation of classic Nim problem. If you don't know what Nim Game is, I suggest you first to learn about it.

In Staircase Nim, there is a staircase with n steps, indexed from 0 to n - 1. In each step, there are zero or more coins. See the figure below:

Two players play in turns. In his/her move a player can choose a step i > 0 and move one or more coins to step i - 1. The player who is unable to make a move lose the game. That means the game ends when all the coins are in step 0.

Now you have to decide who will win the game if both players play optimally.

Observation

We can divide the steps into two types, odd steps, and even steps. Now let's think what will happen if a player A move a coin from an even step to an odd step. Player B can move those coins to an odd position and the state of the game won't change.

But if A move a coin from an odd step to an even step, similar logic won't work. Because there can be situation where player B won't be able to move those coins to another odd step to restore the state.

From this we can agree that coins in even steps are useless, they don't affect game state. If I am in a winning position and you move a coin from an even step, I will move those coins again to another even step and will remain in a winning position.

Determine Winning Position

Now we agreed that only coins to odd steps count. If you take one or more coins from an odd step and move them to an even step, the coins become useless! Remember even steps are useless, So moving to even step is just like throwing them away. Now we can imagine coins in an odd-step as a pile of stones in a standard Nim game.

Now its easy, just find the xorsum of all odd steps and we are done!

Move the Coins

In the HackerRank problem, there is a tree and each node can contain zero or more coins.

In each move, a player can move one or more coin from a node (which is not the root) to its parent node. If a player can't make a move, he/she loses the game.

This is same as Staircase nim but on a tree. You just need to calculate the distance between each node and the root. Now find the xorsum of all odd distance nodes. This can be done using a dfs, complexity O(V + E).

How to answer Alice's Questions?

Now, let's discuss updating the xorsum for each question. Suppose d₁ is the distance between 1 and u. For node u, you must remove the edge between u and p(u) and add an edge between u and v. Suppose d₂ is the new distance between u and 1; if d₁%2 = d₂%2, it won't change the xorsum because odd distance nodes still have odd distances (the same is true for even distance nodes).

If d₁%2! = d₂%2, all the odd distance nodes in subtree u will become even distance nodes, and all the even distance nodes in subtree u will become odd distance nodes. If you save the xorsum of odd and even distance nodes separately, you can easily update it for each question.

A question will be invalid if u and v belong to the same subtree. You can then easily find that using the finishing time in depth-first-search. Some did it by finding LCA but that's too much.

The complexity of answering each question is O(1).

That's all! I will be grateful if you point out the mistakes.

A Game Theory Contest

There will be a multi-day Game Theory Contest in HackerRank on 13th May, targeted mainly to the one who just started learning game theory but last two days will contain some harder problems.

The contest is prepared by allllekssssa, forthright48 and me (with the help of wanbo, as always). Hope to see you in the contest!

Hi, I would like to invite you to take part in HackerRank HourRank-8 on 2nd May.

HourRank is an one hour long programming competition. In this round, there will be only 3 problems. We tried to make it interesting for both beginners and experts.

The authors of this round are tunyash, forthright48 and me. Thanks for wanbo for testing the problems.

Top-10 will get a nice HackerRank Tshirt!

Happy Coding!

Update:

Score of the problems are 25-50-75.

Update:

The contest has ended, congrats to the winners.

Special congrats to uwi for solving all the problems.

Hello CodeForces Community!

I am glad to share that HackerRank's World Codesprint April is scheduled on 29-April-2016 at 16:00 UTC. Contest duration is 24 hours.

Go ahead and register now to show off your coding abilities, and win upto $2000 Amazon gift cards/bitcoins and tshirts. [Note: Winners from US and India will receive Amazon Gift Cards. Winners from other countries will receive equivalent USD amount in bitcoins.]

The problems were prepared by malcolm, Radewoosh, svanidz1, ma5termind and Shafaet. Thanks to wanbo for testing the problems and forthright48 for helping with editorials.

The contest will be rated. If two person gets same score, the person who reached the score first will be ranked higher.

Editorials will be live soon after the contest ends, I invite everyone from experts to beginners to participate and solve challenges. I hope everyone will enjoy the contest.

Edit: The contest is less than 15 minutes away.

Score distribution: 15-20-40-60-60-80-80-100

Update:

The contest is over! Congratulation to the winners:

Ratings will be updated soon. Let us know if you like this round and don't forget to join the next contest HourRank-8!

Update:

Details editorial for Move the Coins problem is posted here.

Hello CodeForces Community!

I am glad to share that HackerRank's World Codesprint is scheduled on 29-January-2016 at 17:00 UTC. Contest duration is 24 hours.

Go ahead and register now to show off your coding abilities, and win upto $2000 Amazon gift cards/bitcoins, medals and tshirts. [Note: Winners from US and India will receive Amazon Gift Cards. Winners from other countries will receive equivalent USD amount in bitcoins.]

The contest is sponsored by Distil-networks, Pampared-chef and Philips. Contest site will be continually updated to reflect upcoming sponsors.

The problems were prepared by malcolm,Errichto,svanidz1, forthright48, and Shafaet. Thanks to wanbo for testing the problems.

The contest will be rated. If two person gets same score, the person who reached the score first will be ranked higher.

Editorials will be live soon after the contest ends, I invite everyone from experts to beginners to participate and solve challenges. I hope everyone will enjoy the contest.

Update: Scoring: 15-25-40-60-80-80-100-100. All the problems will have partial scoring unless explicitly mentioned in problem statement.

Update:

Contest is over. Congrats to the winners.

anta

cgy4ever

Eryx

zeulb

shangjingbo

Hackerrank will contact the winners for prizes very soon! Please share your opinion on the contest in comments, it will help us to improve. The next contest is Hourrank, see you there!

Code the future

Hello CodeForces Community!

I am glad to share that HackerRank's CodeStorm (CodeSprint on Algorithmic Programming Challenges) is scheduled on 29-October-2015 at 16:00 UTC. Contest duration is 24 hours.

Go ahead and register now to show off your coding chops, and win amazing prizes like GoPro HERO4 camera, Bose Speakers, FitBit Charge, HackerRank hoodies and t-shirts. All participants who completely solve one challenge will get $100 of AWS credits.

Also, you'll get an opportunity to connect for a career opportunity with CodeStorm contest sponsors — like ErosDigital, Indeed Prime, Slice, Steelhouse, Sightline Systems, SWATT etc. Contest site will be continually updated to reflect upcoming sponsors.

The problems were created by malcolm, svanidz1, Timur_Sitdikov and Shafaet. Thanks to wanbo and allllekssssa for testing the problems.

The contest will be rated. If two person gets same score, the person who reached the score first will be ranked higher.

Editorials will be live soon after the contest ends, I invite everyone from experts to beginners to participate and solve challenges. I hope everyone will enjoy the contest.

Update: The max scores of the problems will be 15-30-50-70-90-90-125. The problems will have partial scoring unless we mention about binary-scoring explicitly in problem-statement.

Update: Some users got automated emails after the contest about prizes. Everyone with rank 11 to 100 will surely get the tshirt as mentioned here, we are investigating why that email went out.

GL&HF

Hello CodeForces Community!

I am glad to share that HackerRank's WorldCup (CodeSprint on Algorithmic Programming Challenges) starts 11-September-2015 at 16:00 UTC.

Go ahead and register now at www.hackerrank.com/worldcup to show off your coding chops, and win amazing prizes like Video chat with HackerRank founders or Ahmed Aly, DJI Phantom Vision Quadcopter, Phantom 2 Vision+ Quadcopter, Apple Sport Watch, HackerRank hoodies and t-shirts! All participants who completely solve one challenge (that’s just 1 out of 6 questions!) will get $100 of AWS credits. Prizes are restricted to University Students Only.

Also, you'll get an opportunity to connect for a career opportunity with WorldCup contest sponsors — Alarm, Asana, Capital One, Fidessa, Ooyala, Shift, Sightline Systems, Wipro Digital, Verizon, Zendesk, Zenefits.

Contest scoring is 25 — 40 — 50 — 75 — 100 — 120. Tiebreaker is person to reach the score.

I invite everyone from experts to beginners to participate and solve challenges. This is going to be a really awesome contest :)

This is a multi-stage team contest. Top 50%* of teams on the Leaderboard qualify to Semi Finals. *All teams whose final score is the same as the team in the 50% rank qualify (including teams ranked lower because of time penalty tiebreaker).

GL&HF

Link

Number of ways to arrange the blocks should be

f(n)=2*f(n-1)+2*f(n-2); //We can fill just one col in two ways or two col in two ways.

But here we need to find: g(n)=f(n)f(0)+f(n-1)f(1)+....+f(0)f(n).

I can find f(n) using matrix expo but can't solve it for g(n).

Thanks for helping.

I was trying to solve this problem: http://codeforces.net/contest/226/problem/B

I am getting the strange error "wrong answer Participant output contains extra tokens".

But i am printing exactly q integers.

rep(st,q)
    {       
       i64 k;
       cin>>k;
       if(k==1) out.pb(k1);
       else out.pb(solve(k));
    }
    if(SZ(out)!=q) q/=0;
    rep(i,SZ(out))cout<<out[i]<<" ";
    puts("");

Here is the full code: http://codeforces.net/contest/226/submission/4082188

Can anyone tell me whats wrong?