Reverse a Stack using Recursion .py

# Python program to reverse a
# stack using recursion

# Below is a recursive function
# that inserts an element
# at the bottom of a stack.


def insertAtBottom(stack, item):
	if isEmpty(stack):
		push(stack, item)
	else:
		temp = pop(stack)
		insertAtBottom(stack, item)
		push(stack, temp)

# Below is the function that
# reverses the given stack
# using insertAtBottom()


def reverse(stack):
	if not isEmpty(stack):
		temp = pop(stack)
		reverse(stack)
		insertAtBottom(stack, temp)

# Below is a complete running
# program for testing above
# functions.

# Function to create a stack.
# It initializes size of stack
# as 0


def createStack():
	stack = []
	return stack

# Function to check if
# the stack is empty


def isEmpty(stack):
	return len(stack) == 0

# Function to push an
# item to stack


def push(stack, item):
	stack.append(item)

# Function to pop an
# item from stack


def pop(stack):

	# If stack is empty
	# then error
	if(isEmpty(stack)):
		print("Stack Underflow ")
		exit(1)

	return stack.pop()

# Function to print the stack


def prints(stack):
	for i in range(len(stack)-1, -1, -1):
		print(stack[i], end=' ')
	print()

# Driver Code


stack = createStack()
push(stack, str(4))
push(stack, str(3))
push(stack, str(2))
push(stack, str(1))
print("Original Stack ")
prints(stack)

reverse(stack)

print("Reversed Stack ")
prints(stack)

# This code is contributed by Sunny Karira