valueAt method
The current value at index (0-based), in O(log n).
Requires 0 <= index < length.
Audited: 2026-06-12 11:26 EDT
Implementation
num valueAt(int index) =>
// Bounds are enforced by rangeSum, so no separate check is needed.
// ignore: no_equal_arguments -- a single-element sum is the degenerate range [index, index]
rangeSum(index, index);