Trace lab in Linked Lists and Pointer Invariants

Mission

Build a singly linked chain and print traversal order.

Learning outcome: Trace a chain from head to null

Correctness contract

Invariant: Every live node is reachable from head exactly once, and the final next reference is null.

Required technique: Build real IntNode links and traverse only by following next references from head.

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

Input and output

Input: n followed by n node values in head-to-tail order. 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 non-negative and is followed by exactly n signed node values.

Before you code

1. Restate the input and output contract, then predict the visible example without running code.
2. Implement the core state transition: Build real IntNode links and traverse only by following next references from head.
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 3 6 9 12

Sample output

3 6 9 12

Why the sample works: Visible walkthrough for the ordinary non-trivial path. Following next from head visits each reachable node exactly once in chain order. Input `4 3 6 9 12` therefore produces `3 6 9 12`.

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.