42 push_swap

Core Part

Task

Given an unsorted stack a containing unique integer values provided as command line arguments, the task is to sort a using only the following instructions and an empty auxiliary stack b. The program should output the instructions, each separated by a newline character. The objective is to minimize the number of instructions.

Code	Action	Code	Action
sa	swaps the first 2 elements of stack a	ra	shifts all elements of a one up
sb	swaps the first 2 elements of stack b	rb	shifts all elements of b one up
ss	performs sa and sb	rr	performes ra and rb
pa	moves the first element of b to the top of a	rra	shifts all elements of a one down
pb	moves the first element of a to the top of b	rrb	shifts all elements of b one down
		rrr	performes rra and rrb

Utilization

git clone https://github.com/michmos/42_push_swap.git && cd 42_push_swap
make

./push_swap 3 1 2 2147483647 -2147483648

Algorithm

The basic idea of my algorithm is to always push that element of a which requires the minimum rotation in a and b whilst keeping b in descending order. The following visualization was not part of the project and just serves the purpose of illustrating the algorithm. It was being created using .

Sorting 100 random numbers:

Bonus Part

Task

The task is to create a checker program that reads instructions from the standard input and checks whether these result in a sorted stack. It accepts the same command-line arguments as the core program. Valid input are the instructions given in the table above ("sa", "sb" ...)

Utilization

1. providing instructions yourself:

   make checker
   

   ./checker 3 1 2 2147483647 -2147483648
   

   Terminate stdin with ctrl+d when all instructions are provided

2. piping output of core into checker:

   For the last step you need to be in bash

   make push_swap && make checker
   

   ARG="4 67 3 87 23"; ./push_swap $ARG | ./checker $ARG