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Module DS-02DSJAVA

Rotation Window

DSJAVA β€’ Data Structures and Algorithms in Java

Browser-only practice

Problem Statement

Application lab in Arrays and Dynamic Lists

Mission

Rotate a list left by k positions.

Learning outcome: Apply modular indexing to rotate a list

Correctness contract

Invariant: Elements occupy indexes 0 through size - 1, and size never exceeds capacity.

Required technique: Normalize k and place each original value at its modular destination without calling a library rotation routine.

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

Input and output

Input: n, then n integers, then a non-negative rotation count k. 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 positive.
  • The rotation count is non-negative.

Before you code

  1. Restate the input and output contract, then predict the visible example without running code.
  2. Implement the core state transition: Normalize k and place each original value at its modular destination without calling a library rotation routine.
  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

5 1 2 3 4 5 2

Sample output

3 4 5 1 2

Why the sample works: Visible walkthrough for the ordinary non-trivial path. After reducing k modulo n, output position i reads the original value at (i + k) modulo n. Input `5 1 2 3 4 5 2` therefore produces `3 4 5 1 2`.

Progressive hints

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

Open hint 1

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

Open hint 2

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

Open hint 3

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

Constraints

Input contract: n, then n integers, then a non-negative rotation count k.

  • n is positive.
  • The rotation count is non-negative.

Required technique: Normalize k and place each original value at its modular destination without calling a library rotation routine.

Output contract: Print the requested sequence on one line with single spaces and no trailing space.

Use Java 8-compatible code only. Keep the public class names and Practice.solve(Scanner sc) signature from the starter files.

Input Format

n, then n integers, then a non-negative rotation count k.

Output Format

Print the requested sequence on one line with single spaces and no trailing space.

Sample Testcases

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Sample #1
Public sample
5 1 2 3 4 5 2
3 4 5 1 2
Visible walkthrough for the ordinary non-trivial path. After reducing k modulo n, output position i reads the original value at (i + k) modulo n. Input `5 1 2 3 4 5 2` therefore produces `3 4 5 1 2`.

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