clemedon / pushswap

Sort problem

PUSHSWAP 42

The goal of this project is to sort in ascending order numbers with as few operations as possible.

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Index

Usage
Step 1. Init
Step 2. Pre-sort
Step 3. Sort

Usage

Run make in the root of the projet and launch as follows:

./push_swap <numbers_to_sort>

Example: ./push_swap "5 3 9 2 7"

Makefile rules

• make -- compiles philo.
• make clean -- deletes object files.
• make fclean -- deletes object files and philo.
• make re -- fclean + make``.

Init

Input: ./push_swap "5 3 9 2 7"

Init the Stack_A.

Stack_A
5
3
9
2
7

Pre-sort

First we need to find the median so we sort a tab of integer, we pick its middle element as the median.

Tab
9
7
5  ← median
3
2

We push from Stack_A to Stack_B all the elements that are smaller than the median (by repeating ra and using pb when required).

Stack_A             Stack_B
7                   2
9                   3
5

We repeat the two previous steps until there are 2 elements left in Stack_A.

Tab 
7
9  ← new median
5

Stack_A             Stack_B 
7                   5
9                   2
                    3

Sort

Now the pre-sort is done. We need to find the leader and the cost for each element, pa the one that has the cheapest cost and repeat this process.

The cost is the distance to perform to put a Stack_B Element in the right location of the Stack_A.

The leader is the closest value (in terms of value, not distance) between an Element in one Stack and an Element in the other Stack.

Stack_A             Stack_B  |cost|leader|
7 ← leader          5        | 1  | 7    |
9                   3        | 2  | 7    |
                    2        | 2  | 7    |

Move cheapest cost element to Stack_A.

Stack_A             Stack_B  |cost|leader|
5 ← leader          3        | 1  | 5    |
7                   2        | 2  | 5    |
9

Move cheapest cost element to Stack_A.

Stack_A             Stack_B  |cost|leader|
3  ← leader         2        | 1  | 3    |
5
7
9

Move cheapest cost element to Stack_A.

Sort done

Stack_A
2
3
5
7
9