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+#+ANKI_DECK: study_deck_02
+#+TITLE: DSA Tricks & Patterns
+
+* Task: Count character frequencies faster than map :dsa:counting:array:string:retrieval::production:
+:PROPERTIES:
+:ANKI_NOTE_TYPE: Basic
+:ROADMAP: [[file:../roadmap.org::*0242. Valid Anagram][0242. Valid Anagram]]
+:END:
+
+** Front
+Write C++ to count character frequencies in a string using a
+fixed-size array instead of ~std::map~ (assume lowercase a-z only).
+
+** Back
+#+begin_src cpp
+std::array<int, 26> freq{};
+for (char c : s) freq[c - 'a']++;
+#+end_src
+
+*Why:* O(1) per access vs O(log n) for ~std::map~. Use when alphabet
+is bounded and small.