Ecosyste.ms: Awesome
An open API service indexing awesome lists of open source software.
https://github.com/anyaschukin/Push_Swap
A bespoke sorting algorithm, on 2 stacks.
https://github.com/anyaschukin/Push_Swap
42 42-school 42born2code algorithm c push-swap sorting sorting-algorithms
Last synced: about 2 months ago
JSON representation
A bespoke sorting algorithm, on 2 stacks.
- Host: GitHub
- URL: https://github.com/anyaschukin/Push_Swap
- Owner: anyaschukin
- Created: 2018-04-17T16:57:11.000Z (over 6 years ago)
- Default Branch: master
- Last Pushed: 2018-09-06T21:01:25.000Z (over 6 years ago)
- Last Synced: 2024-08-01T10:20:57.966Z (4 months ago)
- Topics: 42, 42-school, 42born2code, algorithm, c, push-swap, sorting, sorting-algorithms
- Language: C
- Homepage:
- Size: 3.8 MB
- Stars: 34
- Watchers: 0
- Forks: 4
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
Awesome Lists containing this project
- 42-resources - Push_Swap
README
# Push_Swap
#### Final Score 105/100
## Challenge
Sort a random list of integers using the smallest number of moves, 2 stacks
and a limited set of operations.
You start with two empty stacks: **a** and **b**. You are given a random list of integers via command line arguments.
Only these moves are allowed:
- `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 last element becomes the first one.
- `rrb` : reverse rotate b - shift down all elements of stack b by 1. The last element becomes the first one.
- `rrr` : `rra` and `rrb` at the same time.
At the end, **stack b** must empty empty and all integers must be in **stack a**, sorted in ascending order.
## The Project
Create two programs: ```checker``` and ```push_swap```.
The ```checker``` program reads a random list of integers from the stdin, stores them, and checks to see
if they are sorted.
The ```push_swap``` program calculates the moves to sort the integers – *pushing, popping, swapping* and *rotating*
them between **stack a** and **stack b** – and displays those directions on the stdout.
You can pipe ```push_swap``` into ```checker```, and ```checker``` will verify that ```push_swap```'s instructions were successful.
Both programs must mandatorily parse input for errors, including empty strings, no parameters,
non-numeric parameters, duplicates, and invalid/non-existent instructions.
**Push_Swap** must conform to the [42 Norm](https://cdn.intra.42.fr/pdf/pdf/960/norme.en.pdf).
Using normal ```libc``` functions is strictly forbidden. Students are however, allowed to use: ```write```, ```read```, ```malloc```, ```free```, ```exit```.
It must not have any memory leaks. Errors must be handled carefully.
In no way can it quit in an unexpected manner (segmentation fault, bus error, double free, etc).
## Approach
I stored all integers parsed into the stack in a **doubly-circular linked list**. This permitted me to access both the top and bottom of each stack (**a** and **b**) in the fewest number of moves, giving me the most efficient access to sort through all integers.
```./push_swap``` writes recommended moves to the ```stdout```, which ```./checker``` then reads off the ```stdin``` and parses. I used a **jump table** to parse the moves and launch the corresponding function. This was much more efficient than an ```if tree```, and triggered an error message for invalid input.
To try this out, launch ```./checker```. To push an integer to **stack b**, type ```pb``` and hit ‘enter’. To see if a combination of moves has sorted the stack, type ```control D``` to finish, and the ```./checker``` will display “OK” for sorted or “KO” for unsorted.
The algorithms in ```./push_swap``` to sort the stack are relatively straight-forward. I had 3 different algorithms: one for 5 numbers or less, one for 100 numbers or less, and one for 500 numbers or less.
For 100 < numbers, I find the median and push everything below the median into **stack b**. Then I identify each the largest and smallest integer in **stack b**, and determine which is most efficient to rotate up/down and push back to **stack a** (along with the specific moves to make that happen). Then I execute those moves.
In this way, integers are pushed back to **stack a** already sorted. I then repeat the process for everything above the median.
For 500 < numbers, I executed the same process but divided **stack a** by quarters instead of median.
## Usage
Run ```make```.
The **checker** program is used as follows:
```c
./checker 5 2 3 1 4
```
```c
./checker "-50 -400 -20 -1 -100"
```
```c
./checker "-22" "35" "40" "-15" "75"
```
The **push_swap** program is used in the same way
```c
./push_swap 5 2 3 1 4
```
You can run the two together using:
```c
ARG=`ruby -e "puts (0..100).to_a.shuffle.join(' ')"`; ./push_swap $ARG | ./checker -v $ARG
```
Note: the **-v (debug) flag** shows the stack status after each operation.
To see push_swap in action, run ```make``` and then the following script:
```
python3 pyviz.py `ruby -e "puts (1..20).to_a.shuffle.join(' ')"`
```
