Push_Swap

Member: 🌜 Ymanzi 🌛

Challenge

Sort a random list of integers using the smallest number of moves, 2 stacks and a limited set of operations.

Instruction set

For the following instructions, if the instruction is not possible, the part of it that can't be executed won't.

Code	Instruction	Action
`sa`	swap a	swaps the 2 top elements of stack a
`sb`	swap b	swaps the 2 top elements of stack b
`ss`	swap a + swap b	both `sa` and `sb`
`pa`	push a	moves the top element of stack b at the top of stack a
`pb`	push b	moves the top element of stack a at the top of stack b
`ra`	rotate a	shifts all elements of stack a from bottom to top
`rb`	rotate b	shifts all elements of stack b from bottom to top
`rr`	rotate a + rotate b	both `ra` and `rb`
`rra`	reverse rotate a	shifts all elements of stack a from top to bottom
`rrb`	reverse rotate b	shifts all elements of stack b from top to bottom
`rrr`	reverse rotate a + reverse rotate b	both `rra` and `rrb`

The Project

Create two programs: checker and push_swap.

checker : takes integer arguments and reads instructions on the standard output. Once read, checker executes them and displays OK if integers are sorted. Otherwise, it will display KO
push_swap : calculates and displays on the standard output the smallest program using Push_swap instruction language that sorts integer arguments received.

Algorythme

The simplest approach is to find the biggest number in stack A move it to stack B, and do it again and again until the stack is empty. Push All the stack B back to A and we would have the numbers sorted from biggest to smallest. This way works but it's inneficient.

Let's say i have a random list of 100 numbers from 0-99. Instead of sorting a big chunck of 100 numbers, it's better to sort 4 chuncks of 25 numbers.

step 1: divide the big list in 4 chuncks (chunk 1 are numbers from 0-24, chunk 2: 25-49, chunck 3: 51-74, chunck 4: 75-99)
step 2: Look for all the numbers from chunck 1 and move them to Stack B. Repeat until all the chuncks are in stack B.
step 3: Push the maximum of the stack B to A, repeat until all the numbers are back to A.
step 4: It's over. Your stack should be sorted

Upgrade

Instead of moving one chunck a time, move the smallest chunck and the biggest one at once

Usage

Run make.

The checker program is used as follows:

  ./checker 5 2 3 1 4

  ./checker "-50 -400 -20 -1 -100"

  ./checker "-22" "35" "40" "-15" "75"

The push_swap program is used in the same way

  ./push_swap 5 2 3 1 4

You can run the two together using:

  ARG=`ruby -e "puts (0..100).to_a.shuffle.join(' ')"`; ./push_swap $ARG | ./checker -v $ARG

Run the visualizer

  python3 pyviz.py `ruby -e "puts (1..99).to_a.shuffle.join(' ')"`

ymanzi / push_swap