Multiplestack

Multiplestack is a data structure concept that stores several independent stacks within a single underlying storage unit, such as an array or a linked structure. It allows multiple LIFO sequences to be manipulated separately while sharing memory resources, which can improve space efficiency when several stacks are needed simultaneously.

Common implementations fall into a few categories. Fixed-partition multiplestack divides the storage into k equal regions, with each region representing one stack. Each region has its own top pointer, and push/pop operations are confined to that region. This approach is simple but can waste space if some regions fill while others remain underused. Flexible or dynamic partitioning lets all stacks share a common pool of free cells. Each stack maintains a top index, and a free-list manages available cells, allowing on-demand expansion of any stack. This improves space utilization but adds complexity and potential resizing overhead. A linked-list-based scheme uses a single array to store elements and, for each stack element, stores a link to the previous element of the same stack. Each stack has its own top index, and growth is limited only by total capacity, at the cost of extra per-element storage.

Operations typically include push, pop, peek, isEmpty, and size, with a focus on constant-time access. Push and pop operate on the specified stack identifier, while maintaining the corresponding top pointer (or index) and, in dynamic schemes, updating the free list or links accordingly. Time complexity for push and pop is generally O(1), subject to memory allocation and potential resizing.

Applications include memory-constrained environments requiring multiple stacks, interpreters and evaluators that use separate operand stacks, and systems needing concurrent or interleaved stack usage without duplicating storage. Multiplestack provides a balance between space efficiency and operational simplicity.