Chairs / Restaurant Order Simulation

Given a sequence of customer / chair events (`C`, `R`, `U`, `L`), simulate the chairs required to seat every customer. The OA-bank version of an order-simulation problem Goldman has recycled across cycles. Requirements For each input string, walk through the characters and track two counters: total chairs ever owned, and chairs currently available for reuse. The character semantics are: C (customer arrives): if a chair is available, reuse it (available--); otherwise buy a new one (total++). R (customer leaves): if any chairs exist, return one to the available pool (available++). U: behaves like C — seat a customer. L: behaves like R — release a chair back to the pool. Return the final total chairs for each string in the input array. public static List<Integer> calculateChairs(String[] arr) Notes Pure single-pass simulation; O(total length) time, O(1) extra space per string. The C / U and R / L symmetry suggests the original problem framed C/R and U/L as two different event types (e.g. two seating zones) — be ready for a follow-up that introduces a third zone. The common solution treats C and U identically; if an interviewer expects per-zone accounting, ask before writing. Edge cases: empty string returns 0; an R or L when there is nothing to release is a no-op, not an error. Preparation Implement once treating all four characters as one combined zone; then refactor with Map<Char, Counter> so a third zone is one line away. Interviewers often ask for the more general form as a follow-up. This is a state-simulation pattern; warm up with LC "Robot Bounded In Circle" (LC 1041) or "Asteroid Collision" (LC 735) for the same mental model.