Day14.cpp

#include <bits/stdc++.h>
using namespace std;
//Deque is a mix of stack and queue: Double end queue: Insert and delete from start or end. Push and pop from end. Header file<deque>
//Sliding window Maximum 
//Circular queue
class CircularQueue{
    int *arr;
    int front;
    int rear;
    int size;
    
    public:
    // Initialize your data structure.
    CircularQueue(int n){
        size = n;
        arr = new int[size];
        front = rear = -1;
    }

    // Enqueues 'X' into the queue. Returns true if it gets pushed into the stack, and false otherwise.
    bool enqueue(int value){
        //to check whther queue is full
        if( (front == 0 && rear == size-1) || (rear == (front-1)%(size-1) ) ) {
            //cout << "Queue is Full";
            return false;
        }
        else if(front == -1) //first element to push
        {
			front = rear = 0;
            
        }
        else if(rear == size-1 && front != 0) {
            rear = 0; //to maintain cyclic nature
        }
        else
        {//normal flow
            rear++;
        }
        //push inside the queue
        arr[rear] = value;
        
        return true;
    }

    // Dequeues top element from queue. Returns -1 if the stack is empty, otherwise returns the popped element.
    int dequeue(){
        if(front == -1){//to check queue is empty
            //cout << "Queue is Empty " << endl;
            return -1;
        }
        int ans = arr[front];
        arr[front] = -1;
        if(front == rear) { //single element is present
            front = rear = -1;
        }
        else if(front == size - 1) {
            front = 0; //to maintain cyclic nature
        }
        else
        {//normal flow
            front++;
        }
        return ans;
    }
};
int main(){
    deque<int> dq;
    dq.push_front(1);
    dq.push_back(2);
    dq.push_front(3);
    dq.push_front(4);
    
    cout<<dq.front()<<"\n";
    cout<<dq.back()<<"\n";

    for(auto i : dq)
         cout<<i<<" ";
    cout<<"\n";
    return 0;
}