YiSu Grain
Oct 29, 2024 · Fundamentals
Why This Design Works and How a Fenwick Tree Simplifies Inversion Counting
The article explains what inversion pairs are, demonstrates a naïve O(n²) counting method, then introduces a smarter right‑to‑left approach using a Fenwick (Binary Indexed) tree with discretization to achieve efficient O(n log n) inversion counting, providing full Python implementations and step‑by‑step examples.
Binary Indexed TreeFenwick treePython
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