https://github.com/llefranc/42_push_swap
School project: implement the best algorithm to sort one stack using another stack (quicksort algorithm).
https://github.com/llefranc/42_push_swap
42 42born2code 42paris 42school push-swap pushswap quicksort quicksort-algorithm stack
Last synced: 4 months ago
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School project: implement the best algorithm to sort one stack using another stack (quicksort algorithm).
- Host: GitHub
- URL: https://github.com/llefranc/42_push_swap
- Owner: llefranc
- Created: 2021-03-08T13:40:18.000Z (over 4 years ago)
- Default Branch: master
- Last Pushed: 2021-10-26T20:13:20.000Z (over 3 years ago)
- Last Synced: 2025-01-16T21:40:22.960Z (5 months ago)
- Topics: 42, 42born2code, 42paris, 42school, push-swap, pushswap, quicksort, quicksort-algorithm, stack
- Language: C
- Homepage:
- Size: 2.22 MB
- Stars: 0
- Watchers: 1
- Forks: 0
- Open Issues: 1
-
Metadata Files:
- Readme: README.md
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README
# push_swap (@42Paris)
> This project was code for MACOS. Here is the [subject][8].
>
*"Because swap_push isn't as natural"*
## About
Push_swap is a project of the mandatory part of the cursus.
It's only made in C and was about creating two programs : one sorting two "special" stacks, and another one checking if the stacks are sorted or not.
We were only allowed to modify the two "stacks", called **stack a** and **stack b**, using a set of instruction :
- `sa` *(swap a)* -- swap the first 2 elements at the top of stack a. Do nothing if there is only one or no elements).
- `sb` *(swap b)* -- swap the first 2 elements at the top of stack b. Do nothing if there is only one or no elements).
- `ss` sa and sb at the same time.
- `pa` *(push a)* -- take the first element at the top of b and put it at the top of a. Do nothing if b is empty.
- `pb` *(push b)* -- take the first element at the top of a and put it at the top of b. Do nothing if a is empty.
- `ra` *(rotate a)* -- shift up all elements of stack a by 1. The first element becomes the last one.
- `rb` *(rotate b)* -- shift up all elements of stack b by 1. The first element becomes the last one.
- `rr` -- ra and rb at the same time.
- `rra` *(reverse rotate a)* -- shift down all elements of stack a by 1. The flast element becomes the first one.
- `rrb` *(reverse rotate b)* -- shift down all elements of stack b by 1. The flast element becomes the first one.
- `rrr` -- rra and rrb at the same time.
In order to succeed, a good comprehension of what is **complexity**, and how the best **sorting algorithms** work was necessary.
## How I solved the problem
For small list of integers (< 5 numbers) I used custom sortings to optimize the number of instructions.
For bigger list, I implemented a variant of quicksort algorithm with several optimizations.
Average nb of insctructions for 100 tests :
- :white_check_mark: : 3 numbers in `1` instruction *(grade 5/5)*
- :white_check_mark: : 5 numbers in `9` instructions *(grade 5/5)*
- :white_check_mark: : 100 numbers in `772` instructions *(grade 4/5)*
- :white_check_mark: : 500 numbers in `5357` instructions *(grade 5/5)*
## Building and running the project
1. Download/Clone this repo
git clone https://github.com/llefranc/42_push_swap.git
2. `cd` into the root directory and run `make`
cd 42_push_swap
make
3. Run `push_swap` with a list of integers in order to print the list of instructions on stdout.
./push_swap 2 1 5 4
4. Run `checker` with a list of integers to solve manually the stack. It will wait for instruction on stdin. Ctrl+D to stop typing instructions
./checker 2 1 5 4
5. Pipe `push_swap` into `checker` with the same list of integers as argument to see if the output of `push_swap` correctly solved the problem
./push_swap 2 1 5 4 | ./checker 2 1 5 4
6. Use `checker` with `-v` option to visualize how push_swap solved the problem
./push_swap 2 1 5 4 | ./checker -v 2 1 5 4
## Sources
- [Quicksort algorithm explained step by step][7]
- [Understanding sorting algorithms and complexity][6]
- [Comprendre la notion de complexité (FR)][4]
- [Visualization of 15 sorting algorithms][3]
- [Explication de quelques algos de tri (FR)][5]
- [Interesting to understang the basics of the project and the algos for stack of 3 / 5 numbers][1]
- [Allows to visualize push_swap in action][2]
[1]: https://medium.com/@jamierobertdawson/push-swap-the-least-amount-of-moves-with-two-stacks-d1e76a71789a
[2]: https://github.com/o-reo/push_swap_visualizer
[3]: https://www.youtube.com/watch?v=kPRA0W1kECg
[4]: https://zestedesavoir.com/tutoriels/621/algorithmique-pour-lapprenti-programmeur/399_presentation-de-la-notion-de-complexite-algorithmique/2020_la-notion-de-complexite/
[5]: https://zestedesavoir.com/tutoriels/621/algorithmique-pour-lapprenti-programmeur/400_premiers-exemples-de-structures-de-donnees-et-dalgorithmes-courants/2024_introduction-au-probleme-du-tri/
[6]: https://medium.com/jl-codes/understanding-sorting-algorithms-af6222995c8
[7]: https://www.youtube.com/watch?v=7h1s2SojIRw
[8]: https://github.com/llefranc/42_push_swap/blob/master/push_swap.en.pdf