Another string-based related problem

This title is not enough to identify one safe algorithm, so begin by clarifying the operation: are we finding a substring, checking an anagram, compressing text, validating parentheses, or transforming characters? Ask for input size, character set, case sensitivity, and whether output order matters. Then state the representation that follows from those answers. For frequency questions, an array of 26 counts is appropriate only for lowercase English letters; otherwise use a hash map. For a sliding-window condition, define precisely what the window counts mean and update them when both pointers move. Test empty strings, a single character, repeated characters, mixed case, and a match at either boundary. Do not silently assume a known LeetCode problem from this vague report. The final Big-O notation depends on the clarified task: a single linear scan is commonly O(n) time and O(k) space for alphabet size k; sorting-based comparison is O(n log n) time.