unipi-CPC-project1

Department of Computer Science, University of Pisa

CPC - Competitive Programming and Contests - Project: Sliding Window Maximum problem

Obtained points: 10/10

Hands-on #01: Sliding Window Maximum problem

In this hands-on, we are going to experiment with different solutions for the Sliding Window Maximum problem. Folder sliding_window_maximum contains two brute force implementations for this problem, tests to check their correctness and a file main.rs to compare their performance on vectors with different sizes.

You are asked to implement the following three asymptotically faster solutions:

• PriorityQueue-based solution with time complexity $\Theta(n \log n)$. Implement this solution in function pub fn heap(nums: &Vec<i32>, k: i32) -> Vec<i32>.
• BBST-based solution with time complexity $\Theta(n \log k)$. Implement this solution in function pub fn bst(nums: &Vec<i32>, k: i32) -> Vec<i32>.
• Deque-based solution with time complexity $\Theta(n)$. Implement this solution in function pub fn linear(nums: &Vec<i32>, k: i32) -> Vec<i32>.

Your goal is to implement these functions in the src/lib.rs file. Their signatures match the requirements at LeetCode to allow you to submit any implementation to this site. Each implementation starts with an ugly let k = k as usize; which is necessary to avoid many annoying casts.

File src/lib.rs contains some tests to check the correctness of you implementation. Feel free to add more tests if needed. You can check the correctness of your implementation by removing the line #[ignore] before a test you are ready to activate. For example,

#[ignore]
#[test]
fn check_bst_version() {
    ...

will skip correctness tests on the bst implementation while

#[test]
fn check_bst_version() {
    ...

will perform it.

To run tests, execute

cargo test

and check the output. As an example, the following output

indicates that the linear version test has successfully been executed while the bst and the pqueue tests have been ignored.

Performance

Once your code successfully passes the complete test suite, you can visualize the performance of your algorithms on random data. Run

cargo run

to execute the code inside main.rs. This measures the execution time of the different implementations by varying the value of k and the size of the vector. Results are reported on a results.csv file. You can look at this file with any other text editor (e.g., nano). We provide a PlotResults.ipynb Jupyter notebook to visualize the results. Install Jupyter lab and run

jupyter-lab

to launch the notebook. Make sure that you have all the required libraries installed by running the cell

!{sys.executable} -m pip install seaborn
!{sys.executable} -m pip install pandas

Seaborn is an awesome data visualization library built on the library Matplolib.

Read the .csv file using Pandas - a popular Python Data Analysis Library -

results_df = pd.read_csv(result_path)

and then plot using

sns.scatterplot(x="k", y="elapsed", hue="Method", data=results_df).

Code optimization

Rust provides various options for compiling code. The command cargo build compiles code in debug mode with the minimum level of optimizations. The command cargo build --release instead optimizes the code at the cost of an increased compile time. Finally, the command RUSTFLAGS='-C target-cpu=native' cargo build --release optimizes the code using all the features (e.g., latest available SIMD instructions set) of your CPU.

We encourage you to experiments with these three different optimization levels.

Best/Worst cases

Performance are measured on randomly initialized vectors (gen_random_vector function in main.rs). Think about the best and the worst input configurations for each of the proposed algorithms and measure their performance by adding customized inputs. What is the difference, in terms of execution time, between the best, the worst, and the average scenario? Write your considerations in your report.

Submission

Submit the file lib.rs and a file SWM_solution_YOUR_NAME.pdf to rossano.venturini@gmail.com by 19/10/2022.

• Source code lib.rs contains your implementations.
• A report SWM_solution_YOUR_NAME.pdf that briefly describes your implementations and provides a detailed analysis of the experimental results. In the report, you should try to answer questions like What's the fastest solution with small values of $k$ and $n$? Why? What's the difference when you increase $k$ or $n$? Do --release and target-cpu=native improve the running time? Is the 1-line idiomatic implementation of the brute force solution slower than the other longer one? Is BST-based solution faster than Heap-based one? Are you able to explain this result? Is linear time solution always the fastest?, and so on. Feel free to modify the Jupyter notebook to better answer those (and other different) questions. The .pdf should be roughly 2 pages (feel free to include plots, if needed).

Before submitting your solutions,

• make sure your implementation successfully passes all the tests.
• use cargo fmt to format your code.
• use cargo clippy to check your code.
• use Grammarly to improve your English and avoid tpyos :-). There is an extension for vscode.

Cheating

Very important! You are allowed to discuss verbally solutions with other students, BUT you have to implement all the solutions by yourself. Thus, sharing implementations with others is strictly forbidden.