The operations stay familiar while the records change. A rota export needs insertion order, a ticket queue needs service from one end, and a score report needs a complete ordering rule. Choose those contracts deliberately instead of reaching for the same collection in every method.
These tasks revisit generic readers and writers, value removal, uniqueness, grouping, deques and comparator ties. Keep duplicate rows when the result is a sequence, and collapse them only when the contract asks for a set or a group. Zero and negative values remain real data unless the prompt rejects them. Review the int-range example before using subtraction in a comparator. There are no guided steps; write a small test of your own for the boundary most likely to break your first attempt.