There was DP. Important Substrings.
How did you implement it using dp? I thought of applying the same algorithm used in finding least number of palindromes but couldnāt figure it outā¦
If u got AC on all subtasks except 3rd try this subtask -
n = 4 k = 1 c = 18
[1ā¦3] [6ā¦11] [10ā¦14] [15ā¦18]
I used prefix sums. At least kind of prefix sums.
I used sliding window 
Increased difficulty doesnt pose any threat because cutoff is decided based on ranking so that the top ~200 people are selected. I faced absolutely 0 issues this time. Different format? Except these, you can report your personal feedback to iarcs but please do not spam this thread by repeatedly asking others to do the same.
Is it really compulsory to have problems on grid graphs and dp? Likeā¦nothing was out of syllabus though. And increased difficulty doesnāt pose any threat because cutoff is decided based on ranking so that the top ~200 people are selected.
Even last years ZCO problems seemed harder than last years INOI problems XD
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@ista2000 Are you sure it is top 200 or are you just pulling out random numbers. If thats the case even people with 10 points would get selected as only ~150 people had even scored any points, looking at the stats on the contest page.
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I think last yearās ZCO was way harder.
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Yeah same, and I think it would have given AC because when I submitted my code it was giving WA, but all my answers were basically 1 less, but I ran out of time lmao RIP
nope. thg, @ista200 used sliding window
I asked arjun arul the intended solution. He told me it was similar to mine. thg, it was a bit different prefix sum
Yes, three different prefix sums for each mod and then a sliding window algorithm.
Anyway, nice.
I donāt think so. I was harder than zco questions <= 2016 but was way easier than inoi or zco 2017
i used lower bounds and prefix sums
It doesnāt matter now. I will try 100x harder next year.