Listaa

Listaa is a hypothetical data structure used in computer science education to illustrate a mutable sequence that combines fast random access with efficient updates. It is not a standard library type but a teaching construct designed to highlight trade-offs between arrays, vectors, and linked lists. The name appears to be a portmanteau of "list" and a generic suffix used in pedagogical naming, and it is encountered in various classroom notes and example code rather than formal specifications.

Design and structure: Listaa conceptually partitions its elements into fixed-size blocks arranged in a linked or array-backed list of blocks. Each block stores a small contiguous subarray and maintains its own size, while a top-level index maps logical positions to a particular block and offset. This layered design allows the structure to grow or shrink without moving all existing elements and enables localized reallocation.

Operations: Access by index is intended to be O(1) on average by computing the block and offset. Insertion or deletion at an arbitrary position typically requires shifting elements within blocks and potentially rebalancing the block layout, yielding O(n) time in the worst case but often better in practice for moderately sized blocks. Appends tend to be O(1) amortized. Memory usage includes overhead for block metadata and the indexing structure.

Usage and notes: Listaa serves as an instructional model for discussing space-time trade-offs and the impact of block size and rebalancing strategies. It is not standardized and varies in informal materials. Related concepts include arrays, dynamic arrays, linked lists, and skip lists.