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.