First-time winners in Div 2 who make it to the top 200 for the first time get Amazon Vouchers worth Rs. 750 each. so my question is am i eligible for the prize if i already secured <200 rank in any codechef short contest but there was no prize in that contest

Can you tell number of problems in each division? TheOneYouWant

I haven't recieved prize of last round. No mail, nothing.

There was an announcement about stack limit in August Cook-Off contest page, but not this time. Has the problem been fixed? If not, it would be better to write it in codechef as well as in codeforces.

I doubt they can even distribute these many prizes. I hope I am wrong!

As a setter, ... I guarantee you will enjoy the contest and hope you win the cash-prize!!

Reminder for the contest: about 18 minutes to go! glhf! :)

very very VERY unclear statements

Can I have an explanation for BunnyHop 2nd Test Case , Unable to understand problem statement .

Here is some feedback on the problemset.

• Just a Graph: Ok easy problem. Straightforward to implement, which is a plus considering the number of problems.
• Bunny Hops: Extremely standard problem (and, sadly, with a nontrivial implementation). In a perfect world, a problem such as this one does not appear in a "div1" contest.
• Chef and Deque: Nice medium problem. I had to think a bit before coming up with a $$$O(3^n)$$$ solution. I enjoyed solving this one.
• Longest Spanning Substrings: Ok problem, though it is a bit standard and there is literally no reason to ask for the minimum spanning tree. It is well-known that a suffix-array provides, in pseudo-linear time, the longest common substring between two strings. It was not obvious to me how to generalize this to multiple strings and it required some thinking. Asking to compute the minimum spanning tree does not make any sense. Asking for the sum of the lengths would have been sufficient.
• Min-Max Path: Nice dynamic programming problem. I enjoyed thinking about this one. The statement is clean (albeit rather artificial) and the solution too.
• ABCD: Extremely standard technical problem. Immediately after reading the statement I knew I had to implement a binary-search on the Stern-Brocot tree and I was scared since the binary-lifting (which I learnt here) is cumbersome to implement.
• Sum of Areas: I have not thought enough about this one, so I will not comment. Anyway, the subtask were on the spot.

Overall, the problems felt a bit too standard and I spent the vast majority of the time implementing stuff. In any case, thanks to the authors for the contest!

for CHEFDQE, I iterated over all the prefixes found yet which have the same value modulo M. Was this the intended solution? I was extremely surprised when it passed the tests.

int n, m, ans = INF;
    cin >> n >> m;
    vector<int> a(n + 1);
    rep(i, 1, n + 1) cin >> a[i];
    map<int, vector<int>> past;
    past[0].push_back(0);
    int curr = 0;
    rep(i, 1, n + 1)
    {
        curr = (curr + a[i]) % m;
        int del = n &mdash; i;
        for (auto j : past[curr])
        {
            if ((del & j) == j)
            {
                ans = min(ans, wt(del));
            }
        }
        past[curr].push_back(i);
    }
    if (ans == INF)
        return -1;
    return ans;

Weak test cases on Bunny Hops and Chef and Deque, got AC with $$$O(n ^ 2)$$$ solutions for both.

What is the intended for Bunny Hops? I was trying tree compression but it felt like bad implementation. (compress line graphs from parent -> child to a single node, then height < log(n), so the $$$O(n ^ 2)$$$ idea takes $$$O(n logn)$$$.) Thankfully (as a participant, not as a setter / tester) the brute I was going to use for stressing passed everything but subtask 1 which is easy prefix sums / OEIS.

Also how to solve Chef and Deque? I just submitted a brute for O(n ^ 2) and it got AC — split by modulo, then brute all $$$O(n ^ 2)$$$ indices [l, r] to find those which satisfy l OR (n — r) = (n — r), then take min of bitcount(n — r). If the tests are only random, this should run in $$$O((n / m) ^ 2)$$$. I suspect setters used random $$$m$$$ (which would end up being larger than n on average) and testers didn't realize, which is unfortunate.

Also is there a point for 20 or 30 points of Longest Spanning Substring to be copy paste Suffix Array / Suffix Automata?

I got the last subtask in chef and deque but failed the remaining subtasks. How does that happen? Weak tests?

:(:(:(:( this contest is nightmare for me, how to solve bnyhop?

Ranks and Scores aren't yet updated on the scoreboard!

Why was the problem LNGSUB given in the first place? Just copy paste string suffix automata from cp algorithms and BOOM :))

I lost all my brain cells trying to understand bunny hops

$$$ O( 3^{\log _{2} n} ) $$$ solution for Chef and Deque .

void solve()
{
	int n,m;
	cin>>n>>m;

	vector<int> pre(n+1);
	
	for(int i=1;i<=n;i++){
		cin>>pre[i];
		pre[i]+=pre[i-1];
		pre[i]%=m;
	}

	int ans=1e9;

	for(int mask=0;mask<n;mask++){
		int b=__builtin_popcount(mask);

		for (int s=mask; ; s=(s-1)&mask) {
			if(s+mask>=n)continue;

			int sum=pre[n];
			sum%=m;
			sum-=pre[s];
			sum%=m;
			sum-=pre[n]-pre[n-mask];
			sum%=m;
			sum+=m;
			sum%=m;

			if(sum==0){
				ans=min(ans,b);
			}

			if (s==0)  break;
		}

	}

	if(ans==1e9)ans=-1;

	cout<<ans<<"\n";
}

I used the submask enumeration code from cp-algorthms

Can someone tell what will be the answer to this testcase in "Bunny Hops"

N=4
par: 1 2 3
A: 10 20 30 40
i.e
1->2->3->4 (10->20->30->40) 
Shouldn't it be 6 ? ( {2,1},{3,2},{3,2,1},{4,3},{4,3,2},{4,3,2,1} )
As we can't jump nodes b/w (i,j)

i got 20 rank in this contest, will I get anything? and by what means?

Profile link — https://www.codechef.com/users/arpit_k_pandey

I'm confused since they mentioned completely different rewards in the contest page in codechef website than what you mentioned here.

How do you solve division 1 P4 — Longest Spanning Substrings?

Hey CodeChef Team, I have a concern regarding the time complexity of some problems like Crossing Blocks. I code in java, and wrote an O(n*log(n)), solution the the problem, which in the given time constraints didn't pass. Where as, I can see that my code converted to C++ could pass easily. Please take these things into consideration next time. I know maybe there is an O(n) solution for that problem, still problems are beautiful if they can be solved using different methods and algorithms. Also can someone tell me, How can i append a line after few statement here in CF comments? btw here is my approach for Problem, approach1 approach2. By the way, Thanks for the wonderful Problem set.

For Chef and Deque isn't the time limit tight if $$$O(3^{logn})$$$ was allowed to pass? My solution in C++17 (https://www.codechef.com/viewsolution/50292475) failed and the same in C++14(https://www.codechef.com/viewsolution/50317654) passed right on the time limit. Is C++17 slow on Codechef?

What am I supposed to do to find an editorial at codechef?

Chef and Deque: I had solved this problem with trie. (https://www.codechef.com/viewsolution/50291496) It has better time complexity N*log(max(A[i])).

I faced a weird issue while solving Bunny Hops. My first submission got a runtime error on all test cases(submission1) then in the second submission I commented out #define int ll and 3 test cases passed(submission 2) and finally after I commented out the complete template(all the define statements) I managed to pass the second subtask(submission3). No clue as to why this is happening.

Probably the best contest of this year on codechef!...though I got +0 rating but still the problems were very nice. But if statement could have been more elaborate it would have been better but overall enjoyed the contest!