We use analytics and advertising cookies to understand how the site is used and whether our ads on Facebook and Instagram work. They are set only if you accept. See our Privacy Policy for details.
The window grows from the right until it violates a constraint, then shrinks from the left until it is valid again - each element enters and leaves at most once, giving O(n). The word contiguous in a problem statement is the giveaway. Variable-size windows (longest substring without repeats) and fixed-size windows (max sum of k elements) are the two shapes worth drilling until they are automatic.
"Longest/shortest contiguous subarray or substring satisfying X."
9 problems. Each one runs in an in-browser editor against real test cases, with hints and a worked solution.
The patterns cheat sheet covers all of these in one page - what each one looks like in a problem statement, and the template that follows.