python stack and queue code example

Example 1: python list as queue

# Demonstrate queue implementation using list
 
# Initializing a queue
queue = []
 
# Adding elements to the queue
queue.append('a')
queue.append('b')
print(queue)
 
# Removing elements from the queue
print("\nElements dequeued from queue")
print(queue.pop(0))
print(queue.pop(0))
 
print("\nQueue after removing elements")
print(queue)
 
# print(queue.pop(0)) will raise and IndexError as the queue is now empty

Example 2: python list as stack and queue

def isEmpty(stk): # checks whether the stack is empty or not
   if stk==[]:
      return True
   else:
      return False

def Push(stk,item): # Allow additions to the stack
   stk.append(item)
   top=len(stk)-1

def Pop(stk):
   if isEmpty(stk): # verifies whether the stack is empty or not
      print("Underflow")
   else: # Allow deletions from the stack
      item=stk.pop()
      if len(stk)==0:
         top=None
      else:
         top=len(stk)
         print("Popped item is "+str(item))

def Display(stk):
   if isEmpty(stk):
      print("Stack is empty")
   else:
      top=len(stk)-1
      print("Elements in the stack are: ")
      for i in range(top,-1,-1):
         print (str(stk[i]))

# executable code
if __name__ == "__main__":
   stk=[]
   top=None
   Push(stk,1)
   Push(stk,2)
   Push(stk,3)
   Push(stk,4)
   Pop(stk)
   Display(stk)

Example 3: python list as stack and queue

#Adding elements to queue at the rear end
def enqueue(data):
   queue.insert(0,data)

#Removing the front element from the queue
def dequeue():
   if len(queue)>0:
      return queue.pop()
   return ("Queue Empty!")

#To display the elements of the queue
def display():
   print("Elements on queue are:");
   for i in range(len(queue)):
      print(queue[i])

# executable code
if __name__=="__main__":
   queue=[]
   enqueue(5)
   enqueue(6)
   enqueue(9)
   enqueue(5)
   enqueue(3)
   print("Popped Element is: "+str(dequeue()))
   display()