Bounded Blocking Queue

Bounded Blocking Queue

Design the state machine behind a bounded blocking queue — a fixed-capacity FIFO where enqueue fails when full and dequeue fails when empty — modelled single-threaded so the logic is testable in isolation.

Requirements

• The queue is FIFO and holds at most capacity items.
• offer(x) enqueues at the tail and returns true; if the queue is full it must not enqueue and returns false.
• poll removes and returns the head item; if the queue is empty it returns -1 (all enqueued values are non-negative, so -1 is an unambiguous "empty" sentinel).
• size returns the current item count, always in 0 .. capacity.
• This is the single-threaded model of a blocking queue: instead of blocking on full/empty we surface it as a false/-1 return, so the ordering and capacity logic can be tested without threads.

API to implement

Implement the class BoundedQueue. The I/O driver is already written in the starter code — it parses the command script below and calls your methods. You only implement the class.

| Command | Returns | Behavior | |---|---|---| | offer <x> | boolean | Enqueue x at the tail and return true, unless the queue is already at capacity, in which case do nothing and return false. | | poll | int | Remove and return the item at the head (FIFO), or return -1 if the queue is empty. | | size | int | Return the number of items currently in the queue. |

Input format

The first line contains Q, the number of operations. The second line contains the constructor argument: capacity — the maximum number of items the queue can hold at once. Each of the next Q lines is one command as listed above. String arguments contain no spaces.

Output format

For each command with a non-void return, print its result on its own line, in order. The driver does this for you — your methods just return values.

This is a design problem: the hidden tests exercise edge cases and interaction sequences, not performance tricks. Model the state cleanly and the tests will pass.

8
2
offer 10
offer 20
offer 30
size
poll
poll
poll
size

true
true
false
2
10
20
-1
0

9
3
offer 5
poll
poll
offer 7
offer 8
size
poll
offer 9
size

true
5
-1
true
true
2
7
true
2