ZIO 2022 Discussion

Hi since I didn’t see a discussion thread for ZIO this year, I decided to make one. Discuss answers/everything else here (I didn’t give ZIO myself though).

Fill your answers on this form https://forms.gle/kYK8SqdGJaz4bjZA6
I’ll share the responses soon.

Form responses - ZIO 2021 Answers (Responses) - Google Sheets


Since I didn’t write ZIO, I would appreciate someone sending brief write-ups for all 4 questions.

Q1) Given a binary string (represented by B and G for boys and girls in question), find the least number of switches (switching position of B and G from any index counts as 2) that maximizes the number of adjacent characters that are not the same.
Q2) Ways to partition an array (consisting of 1,2,3,…,n) into less than or equal to k sub arrays such that for any two sub arrays A and B, there are no elements a,c ∈ A and b,d ∈ B such that a<b<c<d.
Q3) Given a tree with bidirectional weighted edges. Pair nodes such that the sum of distances between each pair is minimized.
Q4) Lexicographically reorder all arrays whose individual elements add up to 1, 2, 3, so on. That is, the reordered list will be: [1],[1,1],[2],[1,1,1],[1,2],[2,1], [3]… and so on. Find the sum of the digits in the 10^6th element of list and product of the digits in the 10^9th element in the list.

These questions are a summarized version and I have skipped over a few details/story-setting.


The form only has space for 3 questions btw, there should be 4 problems with 3 subtasks each.

oh right. fixed

Since confidence levels drop because of ZIO, don’t stress.


Hello all, This us my first time in zio , I am sure that q3 is correct , but q1 might not be . Btw, does anybody have any idea about cutoffs of class 7 and below? I am in class 6

Can Anybody Please share me answers of 2b,2c and 4c

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I think Problem-1 and 3 are so easy. The first two subtasks of problem-4 are also easy However Subtask-3 of problem-4 was little harder. I think most tough problem was 2nd one.

My answers for 2b,2c,4c,3c might be wrong


50 for class 11 (calculated with respect to most frequent answer in each que). Will I pass or should I register for ZCO?

@saarang123 please also add class/grade section in google forms so that we will be able to get an idea of cutoffs for different grades.


f(n+1) = sum{k=1 to n+1} * f(k-1) * f(n+1-k)
a)127 (sum up the road length}
b)40 {sum up the alternatives length}
c)236 {start checking from the ending nodes and then sum up}
a)2 { 1 2 1 1 }
b)20 {2^19 = 19+1 which is 20}
c)864 {3 4 1 3 2 3 1 2 2 1 1 1 1 1 1 1 1 1 }

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@atoner you should register for zco if you are not sure you will pass.

I think answer for problem 1c should be 8. Please explain your approach for problem-1.

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My answer is also coming 8, but some IOITC achievers have told me the answer.
My marks are 45 (Class 9th) and they can be 55 if the answer would be 8.

Is answer key already released i cant find it on offical iarcs website.

4c is 13 i think?

I’m in Class 9 and am expecting 35 (based on the most frequent answer to each question). What are my chances?

Will ZIO results be announced before ZCO is held?

for 1c I got 10.
as far as I remember there were 11 G’s and 8 B’s so the optimal string that could be obtained is
GBGBGBGBGBGBGBGBGGG. I compared this string with the one given in the question and there was a difference of 10 letters, which included 5 G’s and 5 B’s, so I answered it as 10.
However, I am not sure whether this approach is correct.