push_swap_42
This project is the second project of the algorithm branch of the 42 school. The aim of this project is to sort a stack of integers in ascending order, with a limited set of instructions, in as few actions as possible.
Usage
To compile run the command: make
Two executables will be generated:
- push_swap whose goal generate a set of instructions in order to sort the set of integers given as arguments
./push_swap [set of numbers...] - checker which will check whether this set of instructions sorts this set of integers correctly or not
./checker [set of numbers...]The checker program reads the instructions on stdin.
You can also use both executables in a single command by running:
$ARG="set of int..."; ./push_swap $ARG | ./checker $ARG
Instructions
You have at your disposal a stack a you need to sort in ascending order, as well as a stack b.
The following operations are authorized:
- sa : swap a - swap the first 2 elements at the top of stack a.
- sb : swap b - swap the first 2 elements at the top of stack b.
- 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.
- pb : push b - take the first element at the top of a and put it at the top of b.
- 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 flast element becomes the first one.
- rrr : rra and rrb at the same time.
Algorithm
Selection sort
When the stack has a size <= 20, I use a selection sort.
Bucket sort
For bigger stacks, I use a mix of bucket sort and a variant of a selection sort. The numbers of buckets depends on the stack size:
- 5 buckets when stack size <= 100
- 7 buckets when stack size <= 200
- 9 buckets when stack size <= 300
- 10 buckets when stack size <= 400
- 11 buckets for bigger stacks
For each bucket, I push to stack B every number of stack A pertaining to it, always choosing the number that will be the less costly in terms of instructions. I repeat this for each bucket, from the bucket containing to the smallest numbers to the one containing the biggest numbers. Once this step is finished, the stack A is empty.
Then I repeat the following operation until stack B is empty: find the maximum number in stack B, and push it back to stack A.
Test script
In order to test my program and to facilitate the correction, I made a personal script file that can be found in the folder "test_script".
In order to use this script, run the command:./test_script/test_script.sh stack_size number_of_tests
For each test, a new set of numbers of the chosen size (stack_size) will be generated. When a test is done, the number of instructions performed is displayed and whether this set of instructions has succeeded in sorting the stack (✔︎) or not (✖︎). Finally the average of the number of instructions is displayed.
Credits
The bucket sort I implemented was inspired by the algorithm described in this article.