The no-sorting constraint is what makes this interesting.
Clarify assumptions (case sensitivity, character set, whitespace) and edge cases (length mismatch, empty strings). Then propose a frequency count using a hash map or fixed-size array, achieving O(n) time and O(1) or O(k) space. Walk through the algorithm, analyze complexity, and discuss trade-offs versus sorting.
Pro tip: Mention that if the character set is fixed (e.g., ASCII), a 256-element array gives O(1) space and faster constant factors than a hash map. Also, note that early length check avoids unnecessary work.
Ask about case sensitivity, allowed characters, whitespace, and Unicode. Confirm that sorting is disallowed and linear time is required. Check edge cases like empty strings or different lengths.
Explain that you will count character frequencies in the first string and decrement for the second. Use a hash map for general characters or a fixed-size array for a known character set.
Describe initializing the count structure, iterating through the first string to increment counts, then iterating through the second to decrement. If any count goes negative or final counts are non-zero, return false.
State that time is O(n) where n is the length of the strings, and space is O(k) where k is the number of distinct characters (or O(1) for fixed alphabet). Compare with sorting's O(n log n).
Mention that for small strings, sorting might be simpler but not linear. For fixed alphabets, an array is more efficient. Also, note that early length check can quickly reject non-anagrams.
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