Queue using Stack in c++

 

Queue is a linear data structure that follows the First-In-First-Out (FIFO) principle. In other words, the element that is inserted first into the queue will be the first one to be removed. This makes it a great choice for implementing data structures such as waiting lists, task lists, and other similar systems.

In C++, queues can be implemented using a variety of methods, including linked lists and arrays. However, one of the most efficient ways to implement a queue is by using a stack. A stack is a data structure that follows the Last-In-First-Out (LIFO) principle. In other words, the element that is inserted last into the stack will be the first one to be removed.

The basic idea behind using a stack to implement a queue is to use two stacks: one for inserting elements and one for removing elements. The first stack, called the "input stack", is used to insert elements into the queue. The second stack, called the "output stack", is used to remove elements from the queue.

When an element is inserted into the queue, it is pushed onto the input stack. When an element is removed from the queue, it is popped from the output stack. If the output stack is empty, the elements from the input stack are popped and pushed onto the output stack in reverse order. This ensures that the elements are removed in the correct order, as the first element inserted into the input stack will be the last element pushed onto the output stack.

One of the benefits of using a stack to implement a queue is that it is more memory efficient than using a linked list or array. This is because a stack only needs to store a pointer to the top of the stack, whereas a linked list or array needs to store the entire list of elements. Additionally, using a stack for a queue allows for quick insertion and removal of elements, as the time complexity for push and pop operations on a stack is O(1).

Another advantage of using a stack to implement a queue is that it allows for easy implementation of other queue operations, such as checking for the front or rear elements of the queue. The front element of the queue is the top element of the output stack, and the rear element of the queue is the top element of the input stack.

1. Create two stacks, inputStack and outputStack.

2. To insert an element into the queue, use the push() function on the inputStack to add the element to the top of the stack.

3. To remove an element from the queue, check if the outputStack is empty. If it is, pop all elements from the inputStack and push them onto the outputStack in reverse order. This ensures that the elements are removed in the correct order.

4. Pop the top element from the outputStack using the pop() function. This element is the one that was inserted first into the queue.

5. To check the front element of the queue, check if the outputStack is empty. If it is, pop all elements from the inputStack and push them onto the outputStack in reverse order. Return the top element of the outputStack.

6. To check the rear element of the queue, return the top element of the inputStack.

7. To check if the queue is empty, check if both the inputStack and outputStack are empty. If they are, return true. Otherwise, return false.

Overall, this algorithm allows for efficient and effective implementation of a queue using two stacks in C++. The use of stacks allows for quick insertion and removal of elements and easy implementation of other queue operations. Additionally, the use of stacks is more memory efficient than using a linked list or array.

Here is an example of how to implement a queue using two stacks in C++:

#include <stack> 
 class Queue {
 private:
 std::stack<int> inputStack; 
 std::stack<int> outputStack;
 public:
 void enqueue(int x) {
 inputStack.push(x); 
 } 
 int dequeue() { 
 if(outputStack.empty()) {
 while(!inputStack.empty()) 
{ 
 outputStack.push(inputStack.top());
 inputStack.pop();
 }
 } 
 int x = outputStack.top();
 outputStack.pop();
 return x; 
 }
 int front() {
 if(outputStack.empty()) 
{
             
while(!inputStack.empty()) { 
 outputStack.push(inputStack.top());
 inputStack.pop(); 
 }
        }
 return outputStack.top(); 
 }

     
int rear() { 
 return inputStack.top();
 } 
 bool isEmpty() {
 return inputStack.empty() && outputStack.empty();
 } 
};

This implementation of a queue using two stacks in C++ includes the