• Naive solution – fix a starting stand and consecutively include following stands until all brands of ice cream are collected
• This solution runs in at least ~\mathcal O(N^2)~ time ⇒ TLE

• The faster solution is to use two-pointer technique to dynamically enlarge and shorten currently observed sequence of stands
• In the beginning, the sequence is empty
• We must enlarge the sequence if there are still some brands yet to be collected
• Conversely, if all brands have been collected, we can shorten the sequence

We still have two issues to solve:

• First, we need to effectively calculate the amount of different brands that have been collected
• Solution is simple – keep a frequency array of size ~k~, i.e. for each brand, dynamically store the number of collected samples
• Then, while extending the sequence, we increase the count of different brands on the first occurrence of a brand's sample
• While shortening the sequence, we decrease the count of different brands on the last occurrence of a brand's sample
• Secondly, as the stands are positioned circularly, the solution might span over the last stand to the first ones
• It suffices to go through the input twice (imagine as if the input was concatenated with itself once)

• ⇒ By combining mentioned techniques, we obtain an approach that runs in time linear with the amount of samples on the input