> 'finding if a string is a substring of another string' Unless you mean using a "substring" function or regexes... coming up with the naïve O(n^2) algorithm i

> 'finding if a string is a substring of another string' Unless you mean using a "substring" function or regexes... coming up with the naïve O(n^2) algorithm is indeed easy, but finding a fast algorithm like KMP is, I would say, non-trivial? For the "second-largest number in array" it's rather easy to come up with an O(n) algorithm, so I would consider the two cases to be different.