### Theo830's blog

By Theo830, 2 months ago,

1594A - Consecutive Sum Riddle

Hint
Solution
Code (C++)

1594B - Special Numbers

Hint
Solution
Code (C++)

1594C - Make Them Equal

Hint
Solution
Code (C++)

1594D - The Number of Imposters

Hint
Solution
Code 1(C++)
Code 2(C++)

1594E1 - Rubik's Cube Coloring (easy version)

Hint
Solution
Code (C++)

1594E2 - Rubik's Cube Coloring (hard version)

Hint
Solution
Code (C++)

1594F - Ideal Farm

Solution
Code (C++)

• +241

 » 2 months ago, # |   +11 Wow the editorial even before the system tests are finished!
 » 2 months ago, # |   +8 Thx for the fast editorial! :)
 » 2 months ago, # |   +8 Thanks for fast editorial
 » 2 months ago, # |   +8 Thank you for the contest
 » 2 months ago, # |   +9 Great problem set! Thank you
 » 2 months ago, # |   +8 What is the intuition behind B?
•  » » 2 months ago, # ^ | ← Rev. 2 →   0 for all $n \geq 2$ and $k \geq 1$, $n^k > \Sigma_{i=0}^{k-1}n^i$
•  » » 2 months ago, # ^ |   +9 Special number is n base number with only ones. So now we have to figure out how to calculate the k-th one And because it is just a matter of play between ones and zeroes, you are like in a binary number, so the k-th number will be the n-th base number with ones on the same spot as k
•  » » » 2 months ago, # ^ |   0 Got it thanks
•  » » » 2 months ago, # ^ | ← Rev. 2 →   0 can you see my solution for problem B...it is giving tle https://codeforces.com/contest/1594/my
•  » » 2 months ago, # ^ |   0 It was the combination that we can create using powers of a number in increasing order
•  » » 2 months ago, # ^ |   +3 The numbers that we need to form should have distinct powers and their coefficient should be either 1 or 0. For example if we take n = 4 and k = 17 then 17 = (10) base 4. So this would give an intuition that we need to do something with binary strings or bianry representation of a number K as we need coefficient as 0 or 1 of the powers. Now Lets see what we have to do K = 1 in binary = 1 K = 2 in binary = 10 K = 3 in binary = 11 K = 4 in binary = 100 and so on Now lets see how our answer comes out, As we need to find the Kth special number for base n so suppose that above binary strings were formed with base n and then convert them into their decimal equivalent respectively. For example from test cases where n = 3 and k = 4 so now binary representaion of k is 100. Just take this in base n = 3 so it comes out to be 1*3^2 + 0*3^1 + 0*3^0 = 9 and our answer. Similarly take n = 2 and k = 12. So 12 = 1100 in binary. As our base n is also 2 only answer again converts back to 12. You can further take more examples.
•  » » » 2 months ago, # ^ |   0 crystal clear! Thanks
•  » » » 7 weeks ago, # ^ |   0 Thanks man, that's really helpful.Hey if you won't mind, could you please provide some editorials or playlists for bit masking.
•  » » » » 7 weeks ago, # ^ |   0 You can refer to this blog for learning new topics : https://codeforces.com/blog/YouKn0wWho
•  » » » 7 weeks ago, # ^ |   0 thanks
 » 2 months ago, # |   0 Oh , that was realy fast!
 » 2 months ago, # |   -181 Testers for this round be like
•  » » 2 months ago, # ^ |   +129 This is really rude. Testers did their best and gave invaluable feedback. No-one can know every problem that has been created. We are sorry for the situation but testers are not to blame.
•  » » » 2 months ago, # ^ |   0 dumbasses always exist and they have a problem with the universe itself and nothing can be done about it.
•  » » » 2 months ago, # ^ |   -7 i think this was clearly meant as a joke..?? Keep chill guys
•  » » » » 2 months ago, # ^ |   +12 that load of shit barely qualifies as a joke, but okay.
 » 2 months ago, # |   +4 Nice contest. Thank you so much!!!!
 » 2 months ago, # |   +4 That was really nice contest! Great statements, beautiful solution and very fast edutorial! (even faster than sys tests). I really enjoyed these 2h 15m in this contest, thank you!
 » 2 months ago, # |   +4 E2 is pretty interesting I think.
 » 2 months ago, # |   0 Thanks for the fast editorial!
 » 2 months ago, # |   -6 Nice round.
 » 2 months ago, # |   0 excellent contest with an interesting problemset , i got very close to solving 3 problems in a div2 for the first time ever , hopefully gonna do it next time :D
•  » » 2 months ago, # ^ |   +3 same for me too! i was close to solving C and A,B was very interesting :D
 » 2 months ago, # |   +4 D was completely copied from INOI 2021... how can you blatantly copy a problemhttps://www.codechef.com/INOIPRAC/problems/AMONGUS2
•  » » 2 months ago, # ^ |   0 lmao
•  » » 2 months ago, # ^ |   0 how did they do this? 1) You highly underestimate the popularity of among us 2) As pointed by someone in the contest announcement comments that it is a little bit trivial for experienced coders to come up with that idea for the problem... check that comment I am lazy to link it.
•  » » » 2 months ago, # ^ |   +2 yeah but they can atleast put some effort..Like change some thing introduce some different parameter exactly copying a statement is too much
•  » » » » 2 months ago, # ^ |   +35 We did not copy anything and would never ever do that as it ruins the whole point of problemsetting for both authors and contestants. This was an unfortunate coincidence and we are very sorry for it, we will be taking every measure to avoid it in the future.
•  » » » » » 2 months ago, # ^ |   -10 I really appreciate you guys effort...as i think it takes a lot of work to prepare a proper contest and i really respect you all for that.. and as for this it would have happened because of some mistake its just that a single problem, like this ruins your guys effort for all the other problems, and for the people participating it gives unnecessary advantage to some...
•  » » 2 months ago, # ^ |   +3 SUS
•  » » 2 months ago, # ^ |   +11 why y'all downnvoting its not like i am disrespecting ..I am just stating an obvious fact..Really cant get this community sometimes
 » 2 months ago, # |   +4 Can someone please tell me why my solution for E gives wrong answer submission.
•  » » 2 months ago, # ^ |   +1 Your val variable which stores the total number of nodes has been stored modulo 1e9 + 7. And then you are using val as a power. If you are calculating a^b%MOD then b has to be stored not modulo MOD but rather a different number. In this case I think its 1e9+6 so you had to store val modulo 1e9 + 6.
•  » » » 2 months ago, # ^ |   0 can you see my solution for problem B...it is giving tle i don't know why https://codeforces.com/contest/1594/my
•  » » 2 months ago, # ^ |   +9 Your calculation of $val$ is wrong. Fermat's little theorem says $a^{p-1} \equiv 1 \bmod p$, so you have to calculate the exponent modulo $p-1$ (in this case, $10^9 + 6$).
•  » » » 2 months ago, # ^ |   0 Can you please give an example where this calculation of val fails. I am unable to understand why this gives wrong answer?
•  » » » » 2 months ago, # ^ | ← Rev. 2 →   +9 $3^{10}=59049$ mod $5$ is $4$. But $3^0$ mod $5$ is $1$.I hope now you can come up with a similar example for mod $10^9+7$.
•  » » » » » 2 months ago, # ^ |   0 Thanks.
•  » » » » 2 months ago, # ^ |   +2 he is saying that ((x^y)%mod)!=(((x^(y%mod))%mod))
 » 2 months ago, # | ← Rev. 3 →   +16 Better approach for F, for case s > k:For each block of size k,Put, (k-1) continuous ones, and then put (k+1) to avoid subarray with sum k. (1, 1.. k-1 times) (k+1)This is the basic case, when the farm isn't lucky, all other cases of the farm being unlucky will require higher value of s. Sum left, after putting all ones = s - nExtra Sum Required = (n / k) * k (for basic case, described above)if sum_left < extra_sum, then "YES"else, "NO"
•  » » 2 months ago, # ^ |   0 I had the same idea,but I failed to perfectly prove "when the farm isn't lucky, all other cases of the farm being unlucky will require higher value of s."
•  » » 2 months ago, # ^ |   +3 Could you plz tell me how to prove it?thx
•  » » » 2 months ago, # ^ |   +11 Firstly you can porve that if only use k blocks,the minimum n is $2\times k$.Then you will find that the way to construct exactly fits the conclusion above，if only use k blocks,the minimum n is $2\times k$ first. The above conclusion can be proved by using Pigeonhole principle.If there is a legal way that has n less than $2\times k$,it should satisfy that for each $pre_i\bmod k$ must be distinct,because if $pre_i\equiv pre_j\pmod k$,the subarray $[i+1,j]$ will be equal to k,($pre_i<2k$).It is impossible because we have $n+1$ $b_i$,and $n$ $b_i\bmod i$.Then we has already proved the conclusion.Sorry,I'm not certain about whether my proof is correct.Hope it can help you :)
 » 2 months ago, # |   +10 Speedforces, and fast editorial.I missed " if(s==k){ cout << "YES\n"; continue; } " and got F wrong. :(
•  » » 6 weeks ago, # ^ |   0 Can you explain me problem please. I think , I am confuse about what is problem asking.
 » 2 months ago, # | ← Rev. 3 →   +17 For problem $C$ it's just enough to check if any of the chars beetwen $[n/2+1, n]$ (1-indexing) is equal to $c$ , if it's then the answer is 1. $Proof$ : Any number between $[1, x - 1]$ and $[x+1, x*2-1]$ isn't divisible by x, so every index that isn't $x$ ,will be changeable. Time complexity — $O(N)$. My submission — 131189321. Btw, nice contest, thank u!
•  » » 2 months ago, # ^ |   +4 Thank you for this, was trying to understand this in tourist's code lol
•  » » 2 months ago, # ^ |   0 You need to say why it's enough to check $[\frac{n}{2}+1, n]$, because if $x$ in $[1, \frac{n}{2}]$, $2x$ is in the second half, so in order to use $x$ it must be that the character at $2x$ is already correct. So we can use the second half without loss of generality.
•  » » » 2 months ago, # ^ | ← Rev. 2 →   0 Your are right, in order to use x in the $[1, n / 2]$ we need to check $2x,3x..$ as well, but instead of checking $x,2x,3x...$ we just need a maximum $yx$ such that $yx <= n$, and if we mark that $yx$ then every number $x,2x,3x,4x.. •  » » » » 7 weeks ago, # ^ | 0 Awesome perspective! Thanks. •  » » 2 months ago, # ^ | 0 thanks. I got stuck for this for a long time  » 2 months ago, # | 0 Nice problems. Thank you!  » 2 months ago, # | 0 •  » » 2 months ago, # ^ | 0 Thank you sir, very cool.  » 2 months ago, # | 0 Thanks for an amazing contest.I really like problem D and editorial is very good)  » 2 months ago, # | ← Rev. 2 → 0 Video Editorial for Problem D explaining the 2 coloring strategy for bipartite graphsI solved the original problem in contest so I explain my exact thought process which might help some of you.Note that I didn't do this contest because I saw D before starting and didn't want to take an unfair advantage. •  » » 2 months ago, # ^ | ← Rev. 2 → +4 I know, You are a gem! Keep posting such valuable videos. You will surely have a great future ahead. I follow your videos and they are very helpful. Don't mind about the downvoters, such people always exists. •  » » 2 months ago, # ^ | ← Rev. 2 → +2 ak2006 Nice editorial man, keep up the good work. I've seen your content as well it's really educational.  » 2 months ago, # | 0 Can someone please explain E1? •  » » 2 months ago, # ^ | 0 For the root node you have 6 colours to choose from, and for the rest you have 4. Then, the answer must be 6 * (4 ^ ((2 ^ k) — 2)) •  » » » 2 months ago, # ^ | 0 got it. Thank you •  » » » 2 months ago, # ^ | 0 I did with dp i can have ans if n goes till 1e8 its sometimes very interesting to know that the solution was very diffrent[submission:131209883] •  » » 2 months ago, # ^ | 0 You can have DP solution also which is easy to understand . Each node have to be carefully coloured respecting the given condition in problem . My implementation •  » » » 2 months ago, # ^ | 0 Thanks a lot. I was looking for this kind of solution which actually does what the questions says to compute the answer.Thanks again!  » 2 months ago, # | 0 can someone explain me problem B? •  » » 2 months ago, # ^ | 0 Basically, just think like this: For a given n, we need to find the kth integer in base n. Why so? If we need to get to that kth integer, we need to go through all the possible sum of powers of n, which happens to be the process of finding kth integer in base n.To understand it clearly, take n = 2.And for the solution, look for the set bits of k. And add all the powers of n to the set bit positions.Please ask if you need more elaboration on this. •  » » » 2 months ago, # ^ | 0 could you please elaborate it more? •  » » » 2 months ago, # ^ | 0 to get the kth number in base of n , we need to add to sum of powers in the indexes of set bits , for example in case of n=2 , we are getting all natural numbers , but these numbers have a base of 10 , i am confused with this base thing •  » » » » 2 months ago, # ^ | 0 For n=2, we are looking at the kth number in base 2, which goes from 1, 10, 11, 100, 101 and so on.For n=3, we are looking at it in base 3, so 1, 2, 10, 11, 12 and so on. But:the question said that special numbers are sum of different powers, so the base can only contain 0s and 1s, so we will ignore 2, 12, 20 and so on. •  » » » 2 months ago, # ^ | 0 You are a gem. Humanity still remains in this world. •  » » 2 months ago, # ^ | 0 just find binary representation of k and then add n^i where i is all set bits of k.  » 2 months ago, # | 0 How can u think for B . is it number theory or something else ? And how can i be able to solve these type of questions? Pls somebody help me •  » » 2 months ago, # ^ | 0 First, let's see what the array is if n=2.We already know that every integer can be represented via a sum of powers of two (and no two powers are equal). This happens because.. well.. every number has a distinct form in base-2, and the base-2 writing actually indicates you on what powers of two to add.Now, let's see for n=5 for example, what the array will be1 = 1(5) 5 = 10(5) 6 = 11(5) 25 = 100(5) 26 = 101(5)And so on.Observe that the base-5 writing of these numbers looks very similar to the base-2 writing of 1,2,3,4,5... So, we can state the following:If we know the base-2 writing of K, then we can just change the base to n (we keep the number as it was). And from here, I think it's pretty straightforward. •  » » » 2 months ago, # ^ | 0 can u please explain me , like for natural nos like 1 2 3 ... , they have a base of 10 , so y are we refering them to as having base of 2 here •  » » » 2 months ago, # ^ | 0 would you suggest me what should i learn according to me rating ? •  » » 2 months ago, # ^ | 0 It's very basic properties of positional notation (positional numeral system). Read about it.  » 2 months ago, # | 0 Nice problems. Thank you! •  » » 2 months ago, # ^ | 0 Yes,B was very nice problem •  » » » 2 months ago, # ^ | 0 Hey, can you help me here? I am getting the wrong answer for test case 105, 564.Apparently, I am doing something wrong with modulo operator>FastReader s=new FastReader(); int t = s.nextInt(); // Number of test cases for (int i = 0; i 0) { int x = 0; long sum = (long)Math.pow(2, x); while (sum < k) { x++; sum = (sum%mod + (long)Math.pow(2, x)%mod)%mod; } k = (k%mod-(long)Math.pow(2, x)%mod + mod)%mod; ans = (ans%mod + (long)Math.pow(n, x)%mod)%mod; } System.out.println(ans%mod); } •  » » » » 2 months ago, # ^ | 0 I think you should not use Math.pow(). It uses float or double type inside and causes precision loss. Not good at Java, just as my personal opinion. •  » » » » » 2 months ago, # ^ | 0 Noted! I'll attempt it again.  » 2 months ago, # | 0 Excellent contest, System testing was also awesome :D  » 2 months ago, # | ← Rev. 2 → 0 Maybe 1594C has an$O(|s|)$method?Here is my solution.First, if we have a minium i such that$s_i,s_{i+1},...,s_n \neq c$and the answer is$1$operation with a certain$x$, it is obvious that$s_x = c$and$\forall k \in N_+ \wedge kx \leq n, kx < i$.If$i = 1$, we can't find that$x$.If$i \neq 1$, let$a = i - 1$.We can prove that if$a$doesn't match the conditions above, we can't find that$x$. If$a$doesn't match the conditions above and there exists$x$such that$x < a$,$i \leq 2a \leq n$and$\exists k \in N_+, a < i \leq kx \leq a + x < 2a \leq n$, so$x$doesn't match the conditions above.And if and only if$2a > n$,$a$can be the$x$, because$2a > i$,$\forall i \in N_+ \wedge i < a, i$is not divisible by$a$and only at this time$\forall k \in N_+ \wedge k > 2, ka > n$.Then we can use$O(|s|)$to find this$a$and output it, solving the situation when the answer is$1$operation with a certain$x$. •  » » 5 weeks ago, # ^ | ← Rev. 2 → 0 I didn't attend the contest and tried to solve this problem today. It took me some time to come up with the answer that only 3 solutions exists. 0,1 and 2. 0 when all the characters in the string match with the given letter. 1 when any of the characters from 1 <= i <= n/2 and also when any one of the character from n/2 <= i <= n doesn't match the given letter. Else the answer is 2.(when all the characters from n/2 <= i <= n matches the letter). (n being the length of the string. Excuse me if I use s and n for the length interchangibly.) I'm glad that I came up with a better solution than the tutorial. For a newbie its a great win xd  » 2 months ago, # | 0 Great Editorial!!One can check this youtube channel for video editorials: Link  » 2 months ago, # | 0 B harder than E1 !  » 2 months ago, # | ← Rev. 2 → 0 upvoted  » 2 months ago, # | ← Rev. 8 → 0 regarding C — "Make Equal" :Can someone please tell me where my code gives the wrong output? The wrong answer is for test case 74 of preset 2 but I'm not able to see what it is. I've been trying to find my mistake for more than an hour.idea — I tried to check if there is any index > n/2(n/2 + 1 for even numbers ) that has the correct character. If yes, then the required number of x is one. else 2.Link to the submission Code#include using namespace std; typedef long long int ll; #define fastio ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0) #define mod 1000000007 void solve() { ll n; cin>>n; char c; cin>>c; string s; cin>>s; ll mismatches =0; ll numchain =0; bool chain = true; for(ll i=s.size()-1;i>=0;i--) { if(s[i]!=c) { mismatches++; } else { chain = false; } if(chain) { numchain++; } } ll temp; if(n%2==0) { temp = n/2-1; } else { temp = n/2; } if(mismatches==0) { cout<<0<temp) { cout<<2<>t; while(t--) { solve(); } }  •  » » 2 months ago, # ^ | 0 I think your for loop should go from i = 2 to i <= n. You have written i < n. Plz check. •  » » » 2 months ago, # ^ | 0 My apologies, I mistakenly put the wrong code earlier. I have put my original code now. can you please take a look again /\ •  » » » 2 months ago, # ^ | 0 can you please see my problem submission for problem B it is giving tle... •  » » 2 months ago, # ^ | 0 you can link a submission or put the code in a spoiler •  » » » 2 months ago, # ^ | 0 okay, sure •  » » 2 months ago, # ^ | 0 check this test case: 1 13 b aaaaaaabaaaaaoutput :7 answer : 8  » 2 months ago, # | ← Rev. 2 → +22 Contest was actually good, I coded F in O(min(s — n, n) / k), it passed pretests, then I changed in to O(1) but after the round it still works. Strange tests to be honest. Here is my solution https://codeforces.com/contest/1594/submission/131243246 •  » » 2 months ago, # ^ | 0 Actually yes, your code gives TLE on this test Test11000000000000000000 500000000000000000 2  » 2 months ago, # | ← Rev. 2 → +8 I have a solution in problem C that runs in O(|s|) time complexity Firstly, I'll check if all characters in the string are equal to C and if so I will print 0(no need to do any operations). Next, I check if I can use 1 operation only and construct a good string at the end by finding an index such that (s[i] == c) and (i * 2 > n) and doing 1 operation using this index i. Let's divide proving the second step into two parts: Proving that this operation is enough & Proving that if such an index doesn't exist then simply we can't change the whole string to be equal to c in 1 operation. 0) Choosing index i means that all indices n then all indices between i+1 and n are changed to C too. 1) The chosen index must have s[this_Index]=c because we are always not changing any of its multiples including itself and building on this fact we need to choose an index i such that all characters on indices that are multiples of i(if any exists) are equal to c. The thing is that the (largest multiple of i that is <=n) *2 must always be >n hence that an index such that s[this_index] is equal to c and this_index * 2 >n must exist or there will be no way to do it in 1 operation.Finally, if I didn't find such i that can fix the string in 1 operation then I will fix the string in 2 operations by making x = n and this will make all of s[i] = c for 1<=i  » 2 months ago, # | 0 Easier solution for 1594F - Ideal Farm. for (int q = 0; q < Q; q++) { ll S = nl(); ll N = nl(); ll K = nl(); if (S==K) cout << "YES\n"; else if (S < K || S >= N+(N/K)*K) cout << "NO\n"; else cout << "YES\n"; }  •  » » 2 months ago, # ^ | +9 lol I sent the same, now I dont care about the right solution, I am just interested in tests' weakness •  » » 2 months ago, # ^ | ← Rev. 4 → 0 Can you explain it a little? I saw the exact same solution somewhere else but couldn't understand. I have read the editorial though and I understand editorialist's solution. edit — : I think I got it now, this person explained it nicely. comment link  » 2 months ago, # | ← Rev. 2 → 0 I liked problem B. Very nice contest.  » 2 months ago, # | +3 I think it's just simply one of the most interesting contest i've written here. Thanks!  » 2 months ago, # | +2 Can you please explain the end of the tutorial of F? I. e.:"Let m be the maximum number of elements that we can take.We go through the last k elements ([s−k+1,s]) and we count the number of elements that have the same modulo k.For each element in this range, if there are odd elements that have the same modulo, we can't take all of them because for every element x that we add in pre that we also add x+k to b. Thus one element would have a x+k out of range.Therefore we count all the elements that have odd elements with the same modulo k and subtract them from s+k to find m."I can't understand literally anything from here. •  » » 2 months ago, # ^ | +18$m = $the maximum number of elements that we can take among the$[1,s + k]$. (We want to make$pre$of size$n$and$b$of size$n+1$).We only need to build$pre$but there should not same elements in$pre$and$b$.We go through the last$k$elements ($[s−k+1,s]$) and we count the number of elements that have the same modulo$k$.For each element in this range, if there are odd elements that have the same modulo, we can't take all of them (and add them to$pre$) because for every element$x$that we add in$pre$that we also add$x+k$to$b$. Thus one element would have a$x+k$out of range ($x + k > s + k => x > s$which is obviously wrong) .$pre: $($[s−k+1,s]$)($[s−3k+1,s-2k]$)$...b: $($[s+1,s+k]$)($[s−2k+1,s-k]$)$...$Therefore we count all the elements that have odd elements with the same modulo$k$and subtract them from$s+k$to find$m$.I hope that now it's clearer. •  » » 2 months ago, # ^ | +5 The solution means that we need to allocate the elements of$[1, s + k]$into$2n + 1$positions (some elements may not be allocated).Firstly we can observe that for every element$x$assigned to pre there's a corresponding$x + k$assigned to b, this means that the numbers with the same modulo$k$must be allocated even number times. So we can divide all the numbers with the same modulo$k$into the same group. Noticed that if there is an odd number of elements in a group, then the group cannot be fully allocated, so the total number of elements that can be allocated must be subtracted by one. It is easy to figure out how many groups of odd size we have, we can subtract the number of groups with odd size from$s + k$finally we will get the number of elements that we can allocate.But note that$k$must initially be assigned to b (because$b[0]=pre[0]+k=0+k=k$), so the number of groups in which module$k$is equal to$0$must be subtracted by$1$. •  » » » 2 months ago, # ^ | +5 The last paragraph is wrong. When the modulo k is 0 then it's like we take the element 0 in pre and k at pre. Therefore, you again have to subtract 1 when there are odd numbers that have 0 modlulo k. •  » » » » 2 months ago, # ^ | +5 I just consider the elements in$[1,s+k]$, so the element$0$doesn't count.  » 2 months ago, # | +4 in problem D i submit thiscode but it recieved wrong answer it use directed edges but when i convert edges to bidirectionl it get accepts codewhy this happens? •  » » 2 months ago, # ^ | 0 Bruh, how can you still be expert with that amount of solved problems lmffaaaoooo •  » » 2 months ago, # ^ | ← Rev. 2 → 0 I have similar query as well. Did you get to know the reason why this happened? Code with Directed Edges: Directed Code with Undirected Edges: Undirected •  » » » 2 months ago, # ^ | +6 because if 2 says 3 is a liar and 1 says 3 is not a liar then see from first two possibilities are there for 2 and 3 they r 2 is liar while is not or 2 not liar and 3 is. Based on this we can get information about 1 since 1 says 3 is not a liar then if 3 is a liar then 1 is also (see the reverse edge) and if 3 is not a liar then 1 is also not. Thus if we have 2->3 and 1->3 this can be rewritten as 2->3 and 3->1 hence bidirectional •  » » » » 2 months ago, # ^ | 0 yeah, I got your point. Thanks for the explanation. Can you please further tell, why solving with a directed graph gives a wrong answer. I mean, if you have some counter case. •  » » » » » 2 months ago, # ^ | +3 1 4 3 1 2 imposter 3 2 crewmate 4 2 imposter •  » » » » » » 2 months ago, # ^ | +3 your code is giving 3 while the answer should be 2 •  » » » » » » » 2 months ago, # ^ | 0 Thanks a lot.  » 2 months ago, # | ← Rev. 3 → 0 My feedback -I just read F and despite multiple readings couldn't figure out what exactly it means. I tried guessing but couldnt come up with something. I wasnt participating but just decided to look at F in middle of the contest, but would have submitted something on F if I had a soln.- Animal pen doesn't make any sense. Something which animals eat could have been better.- There is no clarification if there are total n pens or if there are n types of pens with infinite quantities of each type.- What exactly do you mean by "empty pen"? You haven't defined what exactly is "empty pen"/"non-empty pen" is.- "all animals in all pens". I tried reading it as "you have to distribute n pens among k animals such that ....." Couldn't come up with something to fill those .... here. Although authors tried to give a formal definition? But a more formal definition would have been better. Formal definitions should be absolutely formal just like the definition after "The problem is the same as" in the editorial. Someone who just reads it should be able to grasp what is being asked and it shouldn't involve references to the story. •  » » 2 months ago, # ^ | +13 Did you perhaps misunderstand what pens are? [Pen](https://en.wikipedia.org/wiki/Pen_(enclosure)) •  » » » 2 months ago, # ^ | 0 Yeah. I did. Thanks. Sorry for my bad English :P •  » » » 2 months ago, # ^ | +8 I've been living in the UK for three years and I've never heard the word 'pen' in this context. Anyone who knows that pen is a thing to write with should be careful about using a word with double meaning... •  » » » » 2 months ago, # ^ | +13 Then what is the word for pen which the UK citizens use? Animal pen is quite common usage. •  » » » » » 2 months ago, # ^ | +24 I think they use the word "pen", but to use it, you must talk about animal pen, which nobody does among city citizens. •  » » » » 2 months ago, # ^ | 0 You guys never came across this?  » 2 months ago, # | +17 Me last night on problem A: Spoiler •  » » 2 months ago, # ^ | 0 I done the same!!! LOL •  » » 2 months ago, # ^ | 0 What does it function means? •  » » » 2 months ago, # ^ | ← Rev. 5 → 0 You mean "ctz"? "Count trailing zeros (in binary)", i.e.,$\operatorname{ctz}(n) =$largest integer$s$such that$2^s$divides$n$. C++ has it in supported architectures as __builtin_ctz, or there is an old algorithm using bitshifts and compares which is essentially hand-coded binary search.Or you can always fall back on the naive$O(\log n)$approach.  » 2 months ago, # | 0 I thought problem E2 was really cool. •  » » 2 months ago, # ^ | 0 can u please explain me the approach i cannot solve it and also do not got it from editorial •  » » » 2 months ago, # ^ | ← Rev. 2 → +5 The idea is that if we have a node$x$, whose color we arbitrarily fix, and nothing in the subtree of$x$is fixed (in the sense that there are no restrictions on nodes below$x$), then we have$4^{sz - 1}$ways to fill out the subtree. There are a lot of nodes of this type; in fact, 99.999% of the nodes are nodes of this type.There are also other types of nodes: nodes in which some child or child of a child, etc is fixed. These cases are a little bit harder and to do so, we can just memoize on its two left and right children. Fix the color on the left child, fix the color on the right child, and then take the sum of the products of sub[left] and sub[right].131252148 •  » » » » 2 months ago, # ^ | 0 Thank u i got it  » 2 months ago, # | 0 A nice round, thanks for the fast editoria!!! •  » » 2 months ago, # ^ | +5 Tou xiang fei chang nice,gei wo zheng xiao le.  » 2 months ago, # | ← Rev. 2 → 0 In problem c,I set p is the c's latest position.if p>n/2,only operation ones,x=p,otherwise,operation twos,x=n-1 and x=n,but I wrong.I can't understand why wrong.131226305 •  » » 2 months ago, # ^ | 0 There is no assignment of 0 when defining P in your code. I think it may be an error here. •  » » » 2 months ago, # ^ | 0 brother 666  » 2 months ago, # | 0 So fast!! Best ever!  » 2 months ago, # | 0 Good thing problem B was from aime lol.i got positive delta.best round ever.easy google •  » » 2 months ago, # ^ | 0 Could u provide a link ?  » 2 months ago, # | 0 in problem E1, "a white node can not be neighboring with white AND yellow nodes", I belive the preposition used should be "or" instead of "and". I only read the formal statement, got confused, and ended up solving another problem for half an hour before realizing how dumb I am :(  » 2 months ago, # | +8 I think problem F's difficulty at most be *1800. •  » » 2 months ago, # ^ | 0 I still don't know solution. I didn't read editorial yet. Only for problems I solved.  » 2 months ago, # | +4 I think in problem C O(nlog(n)) can be reduced to O(n).Notation: n=|s|; c=required char to be set If all s[i]==c then ans=0 Else if at any of these positions (n/2 + 1,....,n), s[i]==c, then using x=i we can set all the rest positions in just 1 operation Otherwise, all of these positions (n/2+1,....,n) will have s[i]!=c. So, they can't be changed in just one operation. So, answer will be 2 with x= n-1 , n •  » » 2 months ago, # ^ | 0 Good job for you to write down this approach here. I have also implemented similar to it during the contest.Link to my submission https://codeforces.com/contest/1594/submission/131210444  » 2 months ago, # | 0 why rating point for this contest is too low? 5 problem only for 7pts :'( •  » » 2 months ago, # ^ | 0 I solved 4 and got a negative delta lmao  » 2 months ago, # | 0 Thanks a lot!  » 2 months ago, # | +6 can some one please tell me how to solve e2 i am unable to get it from editorial(my mistake not of editorial) •  » » 2 months ago, # ^ | ← Rev. 2 → +6 In short, whole idea is to forget about whole tree and find out how many ways to color nodes which are on paths from root to already-colored. Then, multiply by 4 to the corresponding power. And to find out first thing, make dp[v][c] which would tell how many correct ways to color vertex v into color c and its subtree in any colors (without taking into account nodes we're not interested).  » 2 months ago, # | 0 Your text to link here... I tried to solve question C but I got the wrong answer. I read the editorial and my approach was similar to it. Can some pls suggest to me what I missed in my soln. •  » » 2 months ago, # ^ | 0 Try this testcase1 5 b abcdeCorrect sol requires two steps, ur sol prints one •  » » » 2 months ago, # ^ | 0 thanks  » 2 months ago, # | 0 I have finsolved B. But I don't understand why k-th element doesn't equal k? For example, for module 7 and n = 3 we have sequence [0, 1, 2, 3, 4, 5, 6]. What special in 1e9+7?  » 2 months ago, # | 0 Great set of problems with good underlying logics.  » 2 months ago, # | 0 Can someone explain to me Question C? •  » » 2 months ago, # ^ | +4 Video Solutions for all problems from A to E2 : solutions •  » » » 2 months ago, # ^ | 0 Thanks  » 2 months ago, # | 0 Can someone explain how to code problem E1 in java? I have understood the logic but I'm getting TLE error. Please help, thanks in advance. •  » » 2 months ago, # ^ | +3 You should use your own power function. You can see how I coded it in the editorial to implement it yourself.  » 2 months ago, # | 0 More contest at 18 05  » 2 months ago, # | 0 Great Contest. Nice set of problems!  » 2 months ago, # | 0 i was stuck at B so i didn't looked at C oh man C was a easy one  » 2 months ago, # | ← Rev. 3 → 0 There is O(s) solution of problem C — Make Them Equal Explanation: Iterate over the whole string and if the i-th is K then push the index to a vector named good. As we iterating from 0 to n-1, the good is sorted. now if the greatest element aka index of good is greater or equal to the half of the size of the string, then we can prove that this is possible in 1 operation if ( good[good.size() — 1] >= s.size()/2 ) => 1 operation the except cases are same as the Editorial. Here is my submission: 131204546  » 2 months ago, # | 0 in problem F: Why are we going through the last k elements? •  » » 2 months ago, # ^ | +15 I have no idea what editorial is telling about but this should help:Our goal is clearly to construct (judge if this is possible) prefix-sum array such that it has length n + 1, first element is 0, last element is s, the array is strictly increasing and the array doesn't have x and x + k simultaneously for any x (then and only then we would have subarray with length exactly k). Instead we will try to construct longest possible such array (and if it's length would be > n + 1, we can easily "shrink" (decrease it's length) it to obtain construction of array of length exactly n + 1).Now for each rem = 0, 1 .. k-1 let's look how many elements at most of this (prefix) array can be equal to rem MOD k.Clearly for particular "rem" one of optimal constructions is rem, 2k + rem, 4K + rem and so on. So you only need to count how many numbers in interval [0, s] are equal to rem MODULO k. Suppose their count is x. Then you can take at most (x + 1) / 2 of them to the prefix array. Do this for every rem = 0,1 .. k-1 and you will know what is the greatest possible length of this prefix array. The only corner case is when s == k, because you are always forced to contain 0 and s in the prefix sum array as first and last elements. •  » » » 2 months ago, # ^ | 0 Could you please explain why could we easily "shrink" this array? •  » » » » 2 months ago, # ^ | 0 Ok, I figured it out. The elements need to have the same rem, and their difference is already 2K. It would be just greater if we shrink. •  » » » 7 weeks ago, # ^ | 0 probably >=n+1. Thanks for the explanantion. •  » » 2 months ago, # ^ | 0 Because if we don't put the last k elements in pre, b will not have the elements from s to s+k.  » 2 months ago, # | ← Rev. 2 → 0 Those two code are same.The only difference between them is variable type, int and long long int. But one got accepted, another got runtime error. For int type variable got AC, long long int got RE. why ?AC code: 131311594 RE code: 131309828  » 2 months ago, # | +5 Finally become expert QWQ. Continue learning!  » 2 months ago, # | 0 Video Solutions  » 2 months ago, # | 0 I have a doubt in D: My solution is giving Runtime error while using vector of map for storing graph and works fine when I use vector of vector. Can anyone help? Here is link to my solution.  » 2 months ago, # | 0 can anybody see my solution for problem B, it is giving TLE...i don't know why https://codeforces.com/contest/1594/my •  » » 2 months ago, # ^ | 0 update ur solution link correctly •  » » » 2 months ago, # ^ | ← Rev. 2 → 0  » 2 months ago, # | 0 Can anyone plz explain B without binary way?  » 2 months ago, # | 0 I think my solution to the problem C is easier :) •  » » 2 months ago, # ^ | 0 Can you explain the intuition behind your solution ?  » 2 months ago, # | 0 How to solve D by DSU ?  » 2 months ago, # | 0 let the value of k be greater than 64. Can we still use this-> (1LL<  » 2 months ago, # | +3 bad editorial •  » » 2 months ago, # ^ | ← Rev. 2 → +4 Can you be more specific about what you didn't understand? •  » » » 2 months ago, # ^ | 0 If you could write comments on your code explaining why you wrote this specific line then it might be easier to understand your code.  » 2 months ago, # | 0 Thanks for the contest. Nice problems and fast editorial!Question: is it possible to solve B without using bitmasks? •  » » 2 months ago, # ^ | +11 I don't think so. •  » » 2 months ago, # ^ | -14 Yes, check out my solution: https://codeforces.com/contest/1594/submission/131288334. I did it without bitmasks.  » 2 months ago, # | 0 can anybody please explain why is my solution not working for problem d? solution link : https://codeforces.com/contest/1594/submission/131297133 •  » » 2 months ago, # ^ | ← Rev. 2 → 0 I am also getting same verdict on testcase 2 line 40 :(Update: Try this case 4 3 1 2 imposter 3 4 crewmate 2 3 crewmateYour code will give -1. But actual ans is 3.  » 2 months ago, # | +21 Fun fact this is the third problem called Make Them Equal1154B - Make Them Equal1417D - Make Them Equal  » 2 months ago, # | +1 In problem D, What is the intuition behind connecting fake node with A and B nodes if person A said that B is a crewmate. Also, how to do the problem with dp / dsu as it is there in one of the problem tags •  » » 2 months ago, # ^ | 0 because if person A said that B is a crewmate, then A and B must belong to the same type, so if there is fake node between them, when we use dfs to paint node, they must be painted the same color.  » 2 months ago, # | ← Rev. 2 → +8 After hours of reading the Problem F editorial, I still can't understand the last part about finding M. If someone else has the same problem as me, this might help.Suppose we have distributed the array A. Let's build a prefix sum Pre[i] = Pre[i-1] + a[i]. Pre[i] is distinct and increasing. If there are i, j such that Pre[i] = Pre[j] + k then there must exist a segment on A which it's sum equal to k.Now we want to check if there is a way to build Pre[i] that does not exist Pre[i] = Pre[j] + k. Pre[i] is distinct and Pre[i] is a value in range [1...S]. If we chose Pre[i] = x then we can not chose x+k, if we don't chose x+k, we can chose x+2*k .For every p = [0...k-1] (remainder when divided by k), we can take from S number x = t*k+p (t <= S-p/k). The maximum way to choose number x(s) is t=(0, 2, 4, 6,...). Except p=0, the best way to choose is t=(1, 3, 5, 7,..) since Pre[i] > 0. For every p, the maximum way to choose x (or t) is Tp. Now, M = sum of all Tp (p=[0...k]). If M>=n then there is a way that does not exist Pre[i] = Pre[i]+k, the answer is NO, otherwise, the answer is YES.You don't have to count Tp separately, use some modulus and divine operation and you can get M easily.  » 2 months ago, # | +8 Thank you for the contest  » 2 months ago, # | 0 In problem E2, I use priority_queue to process node from bottom to the top, but it lead to TLE in case9, here is my code, anyone can tell me why it fail?  » 7 weeks ago, # | 0 Problem C can be solved in O(|s|) :https://codeforces.com/contest/1594/submission/132498264  » 6 weeks ago, # | ← Rev. 2 → 0 Can anyone help me figure out why my solution is giving RTE in problem D? I am using DSU and small to large merging. 133162809  » 6 weeks ago, # | 0 https://codeforces.com/contest/1594/submission/133176237 why I am getting Wrong answer. which case i haven't considered. •  » » 6 weeks ago, # ^ | 0 It looks like you only use operations for$x = 2$or$x = 3$. In this case, for example, you cannot change the$6$-th position in the string, because$6$is divisible by both$2$and$3\$.
 » 6 weeks ago, # |   0 DIV 2. B The test case explained for n=3 has 1 and 3 in the sequence but how can we write 1 and 3 as the sum of two different powers of n???
 » 5 weeks ago, # | ← Rev. 2 →   0 Hi, here I have an O(n) solution for 1594C - Make Them Equal133993659