Warehouse and Regional Inventory Operations

Maintain quantities of item types at several warehouses. Each warehouse belongs to one fixed region, and every warehouse starts empty. The aligned arrays warehouseIds and regions define this assignment.

For this exercise, process the finite sequence operations in order. Item types are identified by strings. Each operation is one string-array row:

• ["ADD", warehouse, item, quantity]: increase this warehouse's quantity of the item by the positive integer quantity. Return the new warehouse quantity as decimal text.
• ["DELETE", warehouse, item]: remove all stock of that item at this warehouse. Return the removed quantity as decimal text, or "0" when none was stored.
• ["WAREHOUSE_QTY", warehouse, item]: return this warehouse's current quantity of the item as decimal text.
• ["REGION_QTY", region, item]: return the sum of this item's current quantity across all warehouses in the region as decimal text.
• ["MIN_ITEM", region, item1, item2, ...]: among the listed candidate item types, return the item with the smallest regional quantity. Break ties by lexicographically smaller item ID. Repeated candidates do not change the result. With no candidates, return "".

An absent item has quantity 0. A region with no warehouses also has quantity 0 for every item. Every operation that names a warehouse uses a valid warehouse ID; region queries may name an empty region. Warehouse assignments never change. A deletion affects only the named warehouse, not other warehouses that store the same item.