fv99 / push_swap

42 Project about sorting data with two stacks efficiently

push_swap

Exploring sorting algorithms and computational complexity.

You have to write a program named push_swap that takes as an argument the stack formatted as a list of integers. The program must display the smallest list of instructions possible to sort the stack, separated by a ’\n’. The goal is to sort the stack with the lowest possible number of operations

About:

• You have 2 stacks named a and b.
• At the beginning:
  • The stack a contains a random amount of negative and/or positive numbers which cannot be duplicated.
  • The stack b is empty.
• The goal is to sort in ascending order numbers into stack a. To do so you have the following operations at your disposal:

Operations:

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

Bonus:

• Write a program named checker that takes as an argument the stack a formatted as a list of integers.
• It will then wait and read instructions on the standard input.
• Each instruction will be followed by ’\n’.
• Once all the instructions have been read, the program has to execute them on the stack received as an argument.
• If after executing the stack a is sorted and the stack b is empty, then the program must display "OK" followed by a ’\n’.
• In every other case, it must display "KO" followed by a ’\n’ on the standard output.
• In case of error, you must display "Error" followed by a ’\n’ on the standard error.
• Errors include for example:
  • some arguments are not integers
  • some arguments are bigger than an integer
  • there are duplicates
  • an instruction doesn’t exist and/or is incorrectly formatted.