Implement the Fenwick Tree solution for range sum queries.
Key differences from segment tree: - Less code (~20 lines vs ~50) - space vs - Only prefix queries directly; range requires subtraction - Typically faster in practice due to simpler operations When to choose BIT over segment tree: - You only need prefix/range queries (not arbitrary operations) - The operation is invertible (sum: subtract; but min: not invertible) - You want simpler, faster code When to choose segment tree: - Range updates needed (lazy propagation) - Non-invertible operations (min, max, GCD) - More complex queries (k-th element, etc.) Time: . Space: .