File: concatenation-of-array/solution.py

Date: 2026-06-06

Time: 15:47

concatenation-of-array/solution.py

Purpose

This file implements the solution to LeetCode 1929 - Concatenation of Array. Given an integer array nums of length n, it returns an array ans of length 2n where ans[i] == nums[i] and ans[i + n] == nums[i] — effectively nums appended to itself.

Key Components

Solution.maxValue — The method name is wrong. It should be getConcatenation per the LeetCode problem signature. The docstring correctly describes the concatenation behavior, but the method name suggests a different problem (likely a copy-paste error from another solution). Despite the naming bug, the implementation itself is correct: nums + nums produces the right output.

The implementation uses Python's list concatenation operator (+), which creates a new list containing all elements of the left operand followed by all elements of the right. This runs in O(n) time and O(n) space.

Patterns

• Single-class LeetCode convention: Wraps the solution in a Solution class with one public method, matching LeetCode's expected submission format.
• Built-in operator approach: Uses nums + nums instead of manual iteration or itertools.chain — the most Pythonic and readable option for this problem.

Dependencies

• Imports: typing.List for the type annotation. No external dependencies.
• Imported by: concatenation-of-array/test_solution.py exercises this solution. The massive "Imported By" list in the prompt is misleading — those are test files for *other* problems that happen to share the same import pattern (from solution import Solution), not actual consumers of this specific module.

Flow

1. Caller instantiates Solution() and calls maxValue(nums).

2. Python evaluates nums + nums, allocating a new list of length 2n and copying elements from nums twice.

3. The new list is returned.

No branching, no loops, no mutation of the input.

Invariants

• The output length is always exactly 2 * len(nums).
• result[i] == result[i + len(nums)] for all valid i.
• The input list is not modified (list + creates a new list).

Error Handling

None. The function trusts the caller to provide a valid List[int]. This is standard for LeetCode solutions where input constraints are guaranteed by the judge.

Topics to Explore

• [file] concatenation-of-array/test_solution.py — Verify whether tests call maxValue or getConcatenation, which would reveal whether the naming bug is compensated for elsewhere
• [file] concatenation-of-array/review.md — Check if the code review caught the incorrect method name
• [file] build-array-from-permutation/solution.py — Another array-construction problem; compare approaches
• [general] method-naming-consistency — Audit whether other solutions in this repo have mismatched method names vs. LeetCode's expected signatures

Beliefs

• concat-array-wrong-method-name — The method is named maxValue but should be getConcatenation per LeetCode 1929's expected interface
• concat-array-correct-logic — Despite the naming error, nums + nums produces the correct concatenation result for all valid inputs
• concat-array-no-mutation — The solution never mutates the input list; Python's + operator on lists always allocates a new list
• concat-array-linear-complexity — The solution runs in O(n) time and O(n) auxiliary space, which is optimal for this problem