Challenge lab in Queues and Fair Scheduling

Mission

Interleave the first and second halves of an even-sized queue.

Learning outcome: Interleave two queue halves

Correctness contract

Invariant: Dequeue returns the oldest live item while preserving the relative order of all others.

Required technique: Split the even queue into two FIFO halves and alternate one removal from each half.

Complexity target: time O(n); space O(n).

Input and output

Input: An even n followed by n queue values. Whitespace may be spaces or line breaks.

Output: Print the requested sequence on one line with single spaces and no trailing space. Return it as a String; Main.java prints it without adding other text.

Assumptions:

• n is even.

Before you code

1. Restate the input and output contract, then predict the visible example without running code.
2. Implement the core state transition: Split the even queue into two FIFO halves and alternate one removal from each half.
3. Trace the smallest boundary case, verify exact formatting, and justify the authored time and auxiliary-space bounds.

Implement Practice.solve(Scanner sc). Keep every provided filename and public class name unchanged.

Sample input

4 1 2 3 4

Sample output

1 3 2 4

Why the sample works: Visible walkthrough for the ordinary non-trivial path. Values are consumed alternately from the first and second FIFO halves. Input `4 1 2 3 4` therefore produces `1 3 2 4`.

Progressive hints

Try the trace and first milestone before opening a hint. Open them in order.

Hint 1 — Contract: identify what each parsed variable represents and write the invariant beside the loop or recursive method.

Hint 2 — Next step: Trace the smallest non-trivial input and write the structure state after the operation before coding the loop.

Hint 3 — Verification: compare the structure state before and after one operation, then test the smallest valid input and a duplicate or unreachable case when allowed.