### phpduke's blog

By phpduke, history, 4 months ago, ,

Gordian Knot is a Project Euler styled contest that challenges you to untangle the intricate enigmas of mathematics. Feel free to deploy your programming skills to make your life easy. Variety of problem set is slightly different from typical Project Euler styled contests, so we hope that you find the problem set crisp and enjoyable :)

Gordian Knot belongs to same chain of technical events called Threads, which recently organized : Codecraft (on codeforces) & Fool's programming (on codechef). You can follow Threads blog on Quora too, on which we will be adding more articles soon. Presently, we have a unique system design contest called 'SysCraft' running and 'Kings of Machine Learning' lined up too.

Contest Link : https://felicity.iiit.ac.in/threads/gordian-knot/
Start Date : 25th January , 08:00 IST
Duration : 24 hours
Prizes : T-shirts for Indian residents in top 20

NOTE :

• We will release short editorial for 5 most popular problems.
• You can ask for hints here if you are stuck on some problems, during last few hours we will provide hints on selected problems. Others strictly refrain from discussing/commenting about problems or posting hints/solutions.

So, can you solve 24 problems in 24 hours? (We have extra bonus problems)
Get your maths and programming skills brushed up by taking on our challenge and grab one of 20 T-shirts :)

UPDATE :

• Problem statements for P6,10,12,13 have been simplified. Please re-check.
• Solutions for P21 have been re-judged.
• Hint Phase begins! Ask us for hints, We wish to help you solve whole of the problemset :)
• EXTENDED CONTEST till 8 pm today. We really want to see someone solve whole of problemset, hope you make best use of it!
• J.T.J.L. & zimpha unlocked level-7!

RANKLIST :

1. Zimpha
2. J.T.J.L.
3. zeliboba
4. rkm0959
5. akashdeep *
6. jtnydv25 *
7. usaxena95 *
8. triveni *
9. xenny *
10. pokeylope
11. hitman623 *
12. amwat *
13. cerberus97 *
14. golovanov399
15. teja349 *
16. djdolls
17. vercingetorix
18. eygmath
19. pulkitjain41 *
20. shubhiks1032 *

*will get T-shirts! Congratulations. It was great to see a lot of people putting most of their day to the 36hr long contest, thankyou all for that. We had to re-write problem description for clarity in few problems, sorry for the inconvenience. We hope that you enjoyed solving the problems. Feel free to pm if you have suggestions/comments.

We will be publishing 5-popular problems' editorial as promised sooner this week :)

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 » 4 months ago, # |   0 Auto comment: topic has been updated by phpduke (previous revision, new revision, compare).
 » 4 months ago, # |   0 Auto comment: topic has been updated by phpduke (previous revision, new revision, compare).
 » 4 months ago, # | ← Rev. 2 →   +13 Can you share link of last year's contest?
•  » » 4 months ago, # ^ | ← Rev. 2 →   +44 No. But you can see ranklist of past contests. 2017 : min_25 won with quite a difference. Endagorion, anta, arterm, w4yneb0t, geniucos, golovanov399, geniucos, lewin,etc were in top 25. 2016 : tourist, fhlasek, rng_61 finished in top 10.
 » 4 months ago, # |   +10 Is anyone from top 20 eligible for T-shirts or only Indian residents?
 » 4 months ago, # |   0 How to submit an answer for the 6th question?
•  » » 4 months ago, # ^ |   0 is it resolved now ?
•  » » » 4 months ago, # ^ |   0 no, now it's 500 internal server error
•  » » » » 4 months ago, # ^ |   0 Can you go to home page and refresh once ? Is the error still there ?
•  » » » » » 4 months ago, # ^ | ← Rev. 2 →   0 I don't know what the home page is, I refreshed everything many times, still this error
•  » » » » » » 4 months ago, # ^ | ← Rev. 2 →   0 Its fixed now for all. Check P6 now.
 » 4 months ago, # | ← Rev. 2 →   0 Guys, I'd like to note that Q12 is incorrect right now... Solve the problem with i 1,5,9 .. etc.I hope the IIIT ppl look into this problem while I go for lunch :PThis is fixed now, so no need to look into this comment.
 » 4 months ago, # |   +2 Q13: a, b, c should be positive integers, otherwise the answer is not rational.
•  » » 4 months ago, # ^ |   +1 Yes, we missed typing this detail. Updated statement.
 » 4 months ago, # |   0 Auto comment: topic has been updated by phpduke (previous revision, new revision, compare).
 » 4 months ago, # |   0 can you give hints for problem primality testing
•  » » 4 months ago, # ^ |   0 Carmichael Numbers
 » 4 months ago, # |   0 Can you please explain Q4: Recurring Tournament.How is the game being played ?A round robin game is one in which each player plays with every other player. Then how can one player be left ?It would be better if I get an explanation with example.
•  » » 4 months ago, # ^ |   +6 Problem Statement is updated . Please check again . Apologies for the inconvenience caused
 » 4 months ago, # |   0 Should we fill every cell in Q15? Or we could we leave some empty?
•  » » 4 months ago, # ^ |   0 Every cell should be filled
 » 4 months ago, # |   0 I think answer of 8th problem is wrong!!! Please check it again.
•  » » 4 months ago, # ^ |   0 Re-checked. It is correct. Please try again.
•  » » » 4 months ago, # ^ |   +3 Can you please explain the question a bit more.I think there is no upper bound on value of M. But the question asks to maximize M.How can that be possible. And for given n and m pair if more than 1 triplet of (a,b,c) occurs then which one to choose.
 » 4 months ago, # |   +19 What is the probability space in q16?
•  » » 4 months ago, # ^ |   -24 It's mentioned in the question : Find the probability that a randomly chosen line in R**2 cross both circles given that the chosen line crosses C1
•  » » » 4 months ago, # ^ |   +19 I repeat: what is the probability space? Even if we calculate aposterior probability, we need to know what the relative (under the condition that the first circle is intersected) probability distribution is. I can think of several distinct distributions, and each of them seems to me equally possible to be meant.
•  » » » » 4 months ago, # ^ |   0 I agree, statement is unclear
•  » » » » 4 months ago, # ^ |   +3 The space which is being meant here is the angle with X-axis, and value of y at x = 0, which makes sense but should be mentioned clearly.
•  » » » » » 4 months ago, # ^ |   0 What do you mean by "angle and value at x = 0"? One can derive from this that 1) there are no vertical lines (and we haven't fixed the positions of the circles), and 2) the angle is distributed equiprobably on [0, π) (which indeed makes sense)Can we replace the "y(0)" parameter by the "distance to the first circle's center"?
•  » » » » » » 4 months ago, # ^ |   +3 We can replace y(0) by distance from origin. For lines except those of form x = c, it is the same as choosing y(0), as there exists a bijection from distance from origin to y(0) in case of such lines.
•  » » » » » » » 4 months ago, # ^ |   0 Ok, so the prior distribution of this parameter is "uniform over the reals", but this definition becomes good after taking the posterior distribution, thanks.
•  » » » 4 months ago, # ^ |   0 If a line is tangent to C2, do we consider that it "crosses" C2?
•  » » » » 4 months ago, # ^ |   0 Yes we consider that it crosses C2
 » 4 months ago, # |   0 In problem 13, is (a,b,c) an ordered triplet or unordered triplet?
•  » » 4 months ago, # ^ |   0 unordered
•  » » » 4 months ago, # ^ | ← Rev. 4 →   +1 Strange, as I got it right assuming ordered!EDIT : Unordered doesn't make any sense unless you specify a <= b <= c, or something of that sort, as the bases which they are raised to, are different and order matters here.
•  » » » » 4 months ago, # ^ |   0 PS : It is ordered . There was some confusion among us . Sorry for the inconvenience caused .
 » 4 months ago, # |   0 In Q4, what do you mean by match? As there can be 1 person in group, do we count this as match?
•  » » 4 months ago, # ^ |   +3 If there is only 1 person in group , he is the winner then . Thus there are no matches . Since , it is a knockout tournament , there is a match/game between two individuals and winner of that match goes along and the other is knocked out of the tournament . In case some person is left out i.e he does not get a partner to play with because all other partner in that round are playing with someone else , he automatically goes to the next round . This process continues until one person is left . To know more , you can read up about knockout tournaments .
 » 4 months ago, # |   +37 I think solving all four problems of one level to enter the next is a little too much! Won't be able to attempt a lot of harder problems if you are stuck somewhere
 » 4 months ago, # |   0 Q21:Is it correct that ranges such as [-100000, 100000] are inclusive?
•  » » 4 months ago, # ^ |   0 Yes , they are inclusive
•  » » » 4 months ago, # ^ |   0 Is it correct that A = [g(-1000000), ..., g(1000000), h(-100000), ..., h(100000)] and we couldn't change order of its elements? Word "bag" is confusing.
•  » » » » 4 months ago, # ^ |   0 Yes , it is correct
•  » » » » » 4 months ago, # ^ |   0 Could you explain the definition of B more clearly?
•  » » » » » » 4 months ago, # ^ | ← Rev. 2 →   0 B is just a array of integers whose elements are in strictly decreasing order . The motive is to find such a B that k is minimised .
•  » » » » » » » 4 months ago, # ^ |   0 Darn.. that solves the problem :(
 » 4 months ago, # |   +43 just a small request. After contest is done reveal all the questions and answers.They are very interesting.
 » 4 months ago, # |   0 Q22Should we find F(g(N)) or F(g(N)-1) ?
•  » » 4 months ago, # ^ |   0 F(g(N)).
 » 4 months ago, # | ← Rev. 2 →   +28 Small request: Please extend the contest by 12-24 hours (I wanna sleep)
•  » » 4 months ago, # ^ |   0 I could only work on this contest for 10 hrs :(
•  » » » 4 months ago, # ^ |   +11 Cool. That would do. Thanks.
•  » » » » 4 months ago, # ^ |   +22 I think u are mistaken or in need of some sleep.Please check above comment properly.
•  » » » » » 4 months ago, # ^ |   0 Absolutely. My bad. :P
 » 4 months ago, # | ← Rev. 2 →   +3 Can you atleast open the last section for everybody? I think no one has access to it right now. It'll be such a waste if no-one even tries the problems.
 » 4 months ago, # |   +16 Due to ambiguity in certain problem statements, contest has been extended by 12 hours . It will now end at 20:00(UTC +5:30) . Formal update on the blog to be made soon
•  » » 4 months ago, # ^ | ← Rev. 2 →   +4 I am not sure about correctness of judge answers for Q21 and Q24.UPD. Q24 is ok.
•  » » » 4 months ago, # ^ |   0 Q21 has been rejudged
 » 4 months ago, # |   +3 Constraints for unlocking level 7 has been reduced to solving 3 problems in level 6 as of now . Formal update on blog to happen soon . Stay tuned !
 » 4 months ago, # |   0 Please give one sample case for case 10. Its difficult to interpret. Thanks!
•  » » 4 months ago, # ^ |   0 Can anyone please give a sample case or a hint? Got no replies from yesterday
 » 4 months ago, # | ← Rev. 2 →   0 Please Note : Q21 , "Functional Enigma" , answer has been verified and updated on the judge . Please submit again . Apologies for the inconvenience caused . Also the minimum number of questions to advance to level 7 has been put back to 4 . Formal update on blog to happen soon . Stay tuned ! PS : Q21 has also been rejudged for all submissions
•  » » 4 months ago, # ^ |   0 Can you explain this line for Q21: Let B be the set of integers made from corresponding elements in bag A such that its elements should be in strictly decreasing order How is this example working? A = {2,5,2} then B can be {6,2,1}
•  » » » 4 months ago, # ^ |   0 Check this conversations : http://codeforces.com/blog/entry/57311?#comment-409832
 » 4 months ago, # |   0 In question 19, Intersections : Is it given that function g is continuous ? Nothin is written about g, please clarify.
•  » » 4 months ago, # ^ |   0 No such condition is given.
 » 4 months ago, # |   0 Q27: How many decimal digits should the answer be rounded upto?
•  » » 4 months ago, # ^ |   0 upto 6 decimal places.
 » 4 months ago, # |   0 Auto comment: topic has been updated by phpduke (previous revision, new revision, compare).
 » 4 months ago, # |   0 can you give hint for problem simple primality and problem recurring tourament
•  » » 4 months ago, # ^ |   0 Hint: For recurring tournament, Try to think in opposite direction. i.e Given number of people what will be number of matches.
 » 4 months ago, # |   +7 Is the answer of 28-th problem correct? Can you check it?
•  » » 4 months ago, # ^ |   +4 It is correct.
 » 4 months ago, # |   0 Q25: Can the polygon be self-intersecting?
•  » » 4 months ago, # ^ |   +2 Also should it be convex or not?
•  » » 4 months ago, # ^ |   +3 No. Polygon cannot be self-intersecting.
•  » » » 4 months ago, # ^ |   +5 Should it be convex or not?
•  » » » » 4 months ago, # ^ |   +5 No. It it needn't be convex.
•  » » » » » 4 months ago, # ^ |   0 Should we count polygons which shapes could transformed one into another by rotation?
 » 4 months ago, # |   0 Any hint for Q13: Unusual Fraction and Q16: Art ?And please explain Q8: Drunken Mathematician more clearly. I asked for it yesterday but no response.
•  » » 4 months ago, # ^ |   +1 For Q13 think of substituting something in place of (a,b,c)
•  » » 4 months ago, # ^ | ← Rev. 2 →   0 Hi. On your request, problem statement was updated to simpler and concise explanation yesterday. Check it :) Problem 16 HintSeveral methods. Imagine one circle as composition of several hollow circles(rings). Simulate.
 » 4 months ago, # | ← Rev. 2 →   0 Q28Are there 302 swaps with equal probability or 30·29 / 2 + 30 ? In other words are swaps (a, b) and (b, a) considered equal or not?
•  » » 4 months ago, # ^ |   +9 We can select 2 random indices i,j where i=j or i>j or i
 » 4 months ago, # |   0 Any hint for the triangle problem ? Aren't there infinite options for (a,b,c) ? Is the sum convergent ?
•  » » 4 months ago, # ^ |   0 It is convergent :) It's also very similar to a math competition problem held a few years ago.
•  » » » 4 months ago, # ^ |   0 https://artofproblemsolving.com/community/c7h1171039p5624386PUTNAM 2015 B4 is pretty much the same problem.
•  » » » » 4 months ago, # ^ |   0 Thank You . I will look into it.
 » 4 months ago, # |   0 Actually I also can't make a sense out of Q8. Maybe I'm just stupid but I already spent a lot of time trying to figure it out and grasp how all other people could possibly get it :) Could you please somehow clarify the statement?
•  » » 4 months ago, # ^ |   -9 Нужно мерять весами с двумя чашками.
•  » » 4 months ago, # ^ |   +3 I will restate , let me know if this clears it up. You have to choose N containers. You can also choose capacity of each of these N containers. Example : for N=3, you can choose 3 containers with capacities as {1,2,3}. Or you could have chosen {5,5,500}. You need to measure volume of a given liquid using the N containers you chose. You have to dispose a container after you pour liquid on it. Hence ,there's a range on volume of liquid you can measure for some set of N containers you choose. You optimally choose capacities of containers so as to maximize range of liquid-volumes (which varies from 1 to M) you can measure with your chosen containers.In this case, following equation holds: a*M — bN — c = 0, where a, b, c are non-zero constants & M,N are positive integers. Find 100a + 64b + 36c.
•  » » » 4 months ago, # ^ |   0 I still don't understand. Suppose I have a set of containers of volume : {1,2,4}I can measure 1 L using 1 L container. 2 L using 2 L container. 3 L using (1 and 2 L) container. 4 using 4 L container. 5 using (1 and 4 L container). 6 using (4 and 2 L container) and 7 using (1,2 and 4 L container).Am I wrong ?
•  » » » » 4 months ago, # ^ |   0 No, you aren't wrong here.
•  » » » 4 months ago, # ^ |   +3 Ahhh, what I did not understand was that a,b,c are constants for which the equation holds for any N. Not sure how but I got it after reading your answer even though this part is exactly the same as in the statement. Thank you)
 » 4 months ago, # |   0 Q27 : Please explain how the cake is cut. Do the slices have the center as common point or the chosen point as the common point? Also, how is the numbering done? As in, where do we start numbering?
•  » » 4 months ago, # ^ |   0 No , the slices may not necessarily have center as common point . Numbering can be done starting from any slice (0-indexed or 1-indexed , your wish) , then next number is the slice which is next in the clockwise order and so on . It is just that one guy eats the odd number slices and the other even numbered slices .
 » 4 months ago, # | ← Rev. 2 →   +24 I would say Q24 Trapped Constraints is the best problem I have seen in modular arithmetic. Wow. Wish I had more time to try the last level.
•  » » 4 months ago, # ^ |   0 How is multiplicative order defined without stating what is the mod ? Do we need to assume things mod n ?
•  » » » 4 months ago, # ^ | ← Rev. 3 →   +10 they are just primitive roots of unity. There is no mod atleast for counting the sum of primitive roots.
•  » » » » 4 months ago, # ^ |   0 And the sum of those is just mobius function. This can be shown by cyclotomic polynomials and mobius inversion. So once you get t =  - 1 the rest is simple.
•  » » » » » 4 months ago, # ^ | ← Rev. 2 →   0 How did you solve the max(gcd(pq+1, qr+1, pr+1) part?
•  » » » » » » 4 months ago, # ^ | ← Rev. 3 →   +6 If gcd(pq+1,qr+1,rp+1)=T, it is easy to show that p, q, r are all same mod T and p^2+1 is a multiple of T.With this observation, set q=p+T, and r=p+2T. We now have p+T<=n/3, and we aim to maximize T. First note that the easy sol p=14919, T=14919^2+1 works. Let's prove that no larger T exist. If such T existed, p<=n/3-T<=n/3-14919^2-1<=20000. Also note that p^2+1 cannot equal to T in this case (that case is covered by p=14919, T=14919^2+1) so T must be at most (p^2+1)/2. So T<=(20000^2+2)/2<14919^2+1. Done.
•  » » » 4 months ago, # ^ | ← Rev. 2 →   +4 We are looking at primitive roots of unity, the complex number , where .
•  » » » » 4 months ago, # ^ |   0 I was trying to do the same mod n -_- Now I get this. Thanks :)
•  » » 4 months ago, # ^ |   0 Thankyou. :)
 » 4 months ago, # |   0 How was Q23 supposed to be solved?
•  » » 4 months ago, # ^ | ← Rev. 2 →   +3 For snooker problem Q23, just solve (2, 3) + (A, B) = 20(u, v) + (x, y), where (x, y) is either (5, 6), (5, 14), (15, 6), (15, 14) and . The direction will be the direction of (A, B) wrt origin. This can be shown by reflecting the diagram. (very well known I guess)Find all possible (A, B) with A2 + B2 ≤ d2, and calculate the number of directions. I did this by using std::set.
 » 4 months ago, # |   0 How to solve Q25, Q28? For Q28 I tried analyzing the number of cycles and tried to relate it with the probability but it didn't seem to work :(
•  » » 4 months ago, # ^ |   +9 Q28: only the length of cycles are useful. you can sort the length and consider it as state (there at most 5600+ states). code
 » 4 months ago, # |   0 Is Q3 Lehmer's totient problem? Or am I missing something?
•  » » 4 months ago, # ^ |   0 Just run brute force of what has been written in the problem.
•  » » » 4 months ago, # ^ |   +1 It's http://mathworld.wolfram.com/CarmichaelNumber.html which is well-known.
•  » » » » 4 months ago, # ^ |   0 Okay thanks!
 » 4 months ago, # |   0 How to solve triangle infinite series problem?
 » 4 months ago, # |   +3 How to solve Q.13 Unusual Fraction?
•  » » 4 months ago, # ^ |   +3 see my comment above :)
 » 4 months ago, # |   0 How to solve "Ache din"?Were we supposed to find (a,b) such that gcd(a,b)>1?
•  » » 4 months ago, # ^ |   +2 Total blue points within a square is equal to the number of unique slopes which is equal to number of unique y / x values. Every point x, y where gcd(x, y) is 1 will gives a unique slope. Euler Totient Function for each x (or y since it is symmetric) will give us number of irreducible fractions of the form y / x and that is the number of unique slopes that particular x or y contributes. Summing totient function from 1 to n / 2 will give us number of blue points in 1 / 8th of the square (why?). Multiplying this value by 8 gives us total blue points and subtracting from (n + 1)2 - 1 gives us number of green points for a square of side n.
•  » » » 4 months ago, # ^ |   0 Got it now! Thanks a lot for the response
 » 4 months ago, # |   +13 Could you publish the problems for the entire set, since the contest is done now?
 » 4 months ago, # |   0 Auto comment: topic has been updated by phpduke (previous revision, new revision, compare).
 » 4 months ago, # | ← Rev. 2 →   +17 It was a nice contest. I enjoyed all the problems that I could attempt. Thanks for the interesting problems :) Please make the problems for practice. Or upload them to some judge. That will be so nice of you guys :)
 » 4 months ago, # | ← Rev. 2 →   +28 Thanks for the contest. I participated in this contest last 5 years (or may be more, I don't remember). Good to see that contest became much less buggy than several years ago. Also now you have much better feedback system, updates for unclear statement published rather fast, it was good idea to allow all participants ask about statement right here on codeforces, it was very convenient. You still have issues with last problems like in previous years, probably it is because you are preparing them at night before competition or may be during competition =)In this year problems were easier than in previous years (this is not good), but I like some of them: Q24, Q21, Q13, Q18 (and may be something else, but I could'n see problems now)
•  » » 4 months ago, # ^ |   +27 I'd like to give thanks too, but I want to make some notes about thinks which can be better next time. The list of problems is closed now, so I'll not list everything I could. The problem about 100a + 64b + 36c. First of all, it'd be great if you mentioned what you mean by "measuring". As I understood (only after I passed this task), you meant "one can measure x iff it's possible to put some masses we have onto two parts of a balance scale in such a way that one is heavier than another by exactly x". This definition is far from obvious. The problem Q15, dracarys. When you write "a rectangular board with dimensions 5x10^18" I imagine a (5·1018) × (5·1018) board. You could write "a rectangular board with dimensions 5 and 10^18" or "a rectangular board 5 × 1018". I don't want to get the correct definition just because you used "rectangular" instead of "square" (actually, I asked the correct statement to my friends, they told me). The problem Q16. Every time you talk about probabilities, you must specify the distribution. Otherwise your words make no sense. One can omit this if there is somewhat default distribution (for example, one, reading "chosen randomly from [0, 1)", can accept that the distribution is likely to be uniform), but it's not the case. You can choose a point uniformly from the first circle and then pass a line through it and orthogonal to the radius with this point, and it's one distribution; you can choose angle and distance to the center of the circle uniformly and independently, and this is another distribution. I don't know what you mean by "randomly, given that it passes the first circle". There is NO distribution over lines where the angle is chosen uniformly and the distance to the origin is chosen uniformly. There is no prior distribution for the meant statement. Mathtype. You need it. It could help in the 5 × 1018 problem, it could make the formula "a*m + bN + c = 0" look "am + bn + c = 0, etc. This is certainly not everything I wanted to say, but it is about everything. If talk about the essence of problems, they were good, and some of them were great, so thank you for this.
•  » » 4 months ago, # ^ |   +9 zeliboba. Golovanov399. Thanks for value feedback. We have taken them positively. Here is screenshot of problem-list raw from portal if you wish to add more to your comment or you can wait for a day, we will put up all problems in our new judge we are making to standardize it for upcoming contests.And yes, we agree that we should have spent some time on problem statement itself rather than just spending our times to come up with good ideas for essence of problem setting. Apologies for same.
 » 4 months ago, # |   0 My name is not starred, even though I'm Indian.
•  » » 4 months ago, # ^ |   0 And djdolls is starred. I doubt, if he resides in India.
•  » » 4 months ago, # ^ |   0 Yeah, same for me. I'm also Indian and my name is not starred.
•  » » 4 months ago, # ^ |   0 Yeah, mine too, (because of my handle, I guess).
•  » » 4 months ago, # ^ |   +14 Fixed. Pardon for our bad stalking skills :P
 » 4 months ago, # |   +27 I think the contest was pretty good overall. I have a few complaints though:(i) The problem statements were terrible. In almost every problem, I had to make assumptions not clear from the statement. (ii) I really don't like the rule where you have to solve all of the previous level to move to the next level. Maybe someone doesn't have much time and only wants to try hard problems, or they are stuck at one problem and can solve all other problems of the set. Here, one problem has WAY more impact than it deserves. I think most of the participants would agree here.(iii) The levels were not decided appropriately. There was a problem in level 7 which deserved to be in level 4, and there was one in level 4/5 that deserved to be in 7. There were a lot of such pairs of problems which could easily have exchanged the levels.
•  » » 4 months ago, # ^ |   +3 I agree with all the above points.I was stuck for a long long time in the circle problem. And very late I found out about the probability distribution mentioned here. Similarly, I wished I could solve the harder problems and leave the one problem which I was not getting right. Frustrated enough, I had to leave the contest and when I woke up I realized what was wrong with my approach, but then I had only few minutes (around an hour) time left to solve remaining 7 hard problems.
 » 4 months ago, # |   -12 Since not all the participants in top 20 are indians.Why don't you extent your list a bit. May be till Rank 22 :P
•  » » 4 months ago, # ^ |   +6 It was supposed to be a joke -_-
•  » » 4 months ago, # ^ |   +12 Turns out that we have 2 extra T-shirts left. Congratulations for winning T-shirt :)
•  » » » 4 months ago, # ^ |   +6 Am I being joked back ? :P
 » 3 months ago, # |   +6 "We will be publishing 5-popular problems' editorial as promised sooner this week :)" ?Still waiting.