Implement Queue with Front, Middle, and Back Operations in Python

Suppose, we are asked to implement a queue that can push and pop values at the front, middle, and back.

We have to implement a pair of functions to push and pop for all three cases. We have to implement another function that shows the full queue at a given time.

So, if the input is like

push_from_back(10)

push_from_back(20)

push_from_front(30)

push_from_middle(40)

push_from_front(50)

show_queue()

pop_from_back()

show_queue()

pop_from_front()

show_queue()

pop_from_middle()

show_queue(),

then the output will be [50, 30, 40, 10, 20

[50, 30, 40, 10]

[30, 40, 10]

[30, 10]

To solve this, we will follow these steps −

• array := array representation of the queue

• Define a function push_from_front() . This will take value

  • insert value into array at position 0

• Define a function push_from_middle() . This will take value

  • insert value into array at position (size of array) / 2

• Define a function push_from_back() . This will take value

  • insert value at the end of array

• Define a function pop_from_front() .

  • delete and return the first element from the array if it is not empty

• Define a function pop_from_middle() .

  • delete and return the element at position (length of array - 1) /2

• Define a function pop_from_back() .

  • delete and return the last element from the array

• Define a function show_queue() . This will take no input

  • return array

Example

Let us see the following implementation to get better understanding

class Solution():

   def __init__(self):
      self.array = []

   def push_from_front(self, value):
      self.array.insert(0, value)

   def push_from_middle(self, value):
      self.array.insert(len(self.array) // 2, value)

   def push_from_back(self, value):
      self.array.append(value)

   def pop_from_front(self):
      return (self.array or [-1]).pop(0)

   def pop_from_middle(self):
      return (self.array or [-1]).pop((len(self.array) - 1) // 2)

   def pop_from_back(self):
      return (self.array or [-1]).pop()

   def show_queue(self):
      return self.array

ob = Solution()
ob.push_from_back(10)
ob.push_from_back(20)
ob.push_from_front(30)
ob.push_from_middle(40)
ob.push_from_front(50)
print(ob.show_queue())
ob.pop_from_back()
print(ob.show_queue())
ob.pop_from_front()
print(ob.show_queue())
ob.pop_from_middle()
print(ob.show_queue())

Input

ob = Solution()
ob.push_from_back(10)
ob.push_from_back(20)
ob.push_from_front(30)
ob.push_from_middle(40)
ob.push_from_front(50)
print(ob.show_queue())
ob.pop_from_back()
print(ob.show_queue())
ob.pop_from_front()
print(ob.show_queue())
ob.pop_from_middle()
print(ob.show_queue())

Output

[50, 30, 40, 10, 20]
[50, 30, 40, 10]
[30, 40, 10]
[30, 10]