Special Queue: A Queue Implemented Using Two Stacks

Special Queue: A Queue Implemented Using Two Stacks

Special Queue: A Queue Implemented Using Two Stacks

Introduction

Queues and stacks are fundamental data structures used in computer science and programming. However, what if we could combine the benefits of both data structures into a single efficient data structure? In this article, we will explore a special Queue implementation that utilizes two stacks. This special Queue leverages the Last-In-First-Out (LIFO) property of stacks to store the value of some operation on the elements, allowing us to perform various operations on the Queue efficiently.

The Queue Implementation

Let's take a look at the implementation of the special Queue using two stacks:


    class Queue:
        def __init__(self, init = float('inf'), func = min):
            self.func = func
            self.f = Stack(init, func)
            self.s = Stack(init, func)
            
        def push(self, val):
            self.f.push(val)
            
        def empty(self):
            return self.f.empty() and self.s.empty()
        
        def pop(self):
            if self.s.empty():
                while not self.f.empty():
                    self.s.push(self.f.pop())
                if not self.s.empty():
                    return self.s.pop()
                
        def funcval(self):
            return self.func(self.f.funcval(), self.s.funcval())

Explanation

The special Queue implementation consists of two stacks, denoted as `self.f` and `self.s`. The `self.f` stack is used for push operations, while the `self.s` stack is used for pop operations.

When an element is pushed into the Queue, it is added to the `self.f` stack using the `push` method. The `empty` method checks if both stacks are empty, indicating an empty Queue.

When the pop operation is called, the `pop` method checks if the `self.s` stack is empty. If it is, it transfers elements from the `self.f` stack to the `self.s` stack in a Last-In-First-Out order. This process ensures that the first element pushed into the Queue becomes the first element to be popped, adhering to the Queue's First-In-First-Out (FIFO) behavior. Finally, the top element from the `self.s` stack is popped and returned as the result of the pop operation.

The `funcval` method allows us to evaluate the result of a specific operation on the elements of the Queue. By providing a custom function during the Queue's initialization, we can choose the desired operation, such as sum, product, GCD, LCM, maximum, minimum, and more.

Conclusion

The special Queue implemented using two stacks is a versatile data structure that combines the benefits of queues and stacks. It allows efficient push and pop operations while providing the flexibility to evaluate different operations on the elements. This implementation can be particularly useful when we need to perform calculations or retrieve information based on the elements stored in the Queue. Understanding and utilizing this special Queue can enhance our ability to solve various programming problems efficiently.

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