In this article, we will discuss how to create a dynamic circular queue using a circular array having the following functionality:
- Front(): Get the front item from the queue.
- Back(): Get the last item from the queue.
- Push(X): Push the X in the queue at the end of the queue.
- Pop(): Delete an element from the queue.
Below is the step-by-step illustration:
- Initially, the queue is empty.
- Insert element 1 to the back of the queue.
- Insert elements 2, 3, 4 to the back of the queue.
- Insert elements 5 to the back of the queue.
- Pop 4 elements from the queue.
- Pop 1 element from the queue.
Approach: The idea is to double the size of the array used every time the capacity of the array gets full and copy the elements of the previous array into the new array. Follow the steps below to solve the problem:
- Initialize 4 variables say frontIndex, backIndex, sizeVar, and capacity and an array say arr[] to implement the queue,
- Define a function say Capacity() to find the size of the current array used:
- Return the capacity.
- Define a function say size() to find the count of elements in the queue:
- Return the variable sizeVar.
- Define a function say full() to find if the queue is full or not:
- Return true if sizeVar is equal to capacity. Otherwise, return false.
- Define a function say empty() to find if the queue is empty or not:
- If frontIndex and backIndex are equal to -1 then return true. Otherwise, return false.
- Define a function say Front() to print the front element of the queue:
- Print the element of arr[frontIndex] if queue is not empty().
- Define a function say Back() to print the last element of the queue:
- Print the element of arr[BackIndex] if queue is not empty().
- Define a function say Push(X) to insert an element at the end of the queue:
- If the queue is full then double the size of the current array and copy the elements of the previous array into the new array.
- If queue is empty() then assign frontIndex = backIndex = 0 and then assign X to both arr[frontIndex] and arr[backIndex] and then increment sizeVar by one.
- Else, update backIndex as backIndex = (backIndex+1)%capacity and then assign X to arr[backIndex] and increment sizeVar by one.
- Define a function say Pop() to delete an element at the front of the queue:
- If the queue is empty print “Underflow”.
- Else if sizeVar is equal to 1 then assign -1 to frontIndex and backIndex both and then decrement sizeVar by one.
- Else, Update frontIndex as frontIndex = (frontIndex+1)%capacity and decrement sizeVar by one.
Below is the implementation of the above approach:
C++
// C++ program for the above approach#include <bits/stdc++.h>using namespace std;// Class definition for queuetemplate <class X>class Queue {private: // Stores the frontIndex int frontIndex; // Stores the back Index int backIndex; // Stores the array X* arr; // Stores the sizeof queue int sizeVar; // Stores the size of array int capacityVar = 4;public: // Queue class constructor Queue() { arr = new X[capacityVar]; frontIndex = backIndex = -1; sizeVar = 0; } // Function Methods bool empty(); bool full(); void push(X x); void pop(); X front(); X back(); int capacity(); int size();};// Find the capacity of queuetemplate <class X>int Queue<X>::capacity(){ return capacityVar;}// Find the number of elements// present in Queuetemplate <class X>int Queue<X>::size(){ return sizeVar;}// Function to check if// Queue is empty or nottemplate <class X>bool Queue<X>::empty(){ if (frontIndex == -1 && backIndex == -1) return true; else return false;}// Function to check if the queue// is full or nottemplate <class X>bool Queue<X>::full(){ if (sizeVar == capacityVar) return true; else return false;}// Function to find the front element// of the queuetemplate <class X>X Queue<X>::front(){ // If queue is empty if (empty()) { cout << "Queue underflow" << endl; abort(); } return arr[frontIndex];}// Function to find the last element// of the Queuetemplate <class X>X Queue<X>::back(){ if (empty()) { cout << "Queue underflow" << endl; abort(); } return arr[backIndex];}// Function to insert the element// to the rear end of the queuetemplate <class X>void Queue<X>::push(X x){ if (full()) { // If the queue is full, then // double the capacity capacityVar = capacityVar * 2; // Initialize new array of // double size X* temp = new X[capacityVar]; // Copy the elements of the // previous array in the order of the queue for (int i = 0, j= frontIndex; i < sizeVar; i++){ temp[i] = arr[j]; j = (j+1) % sizeVar; } // update the front and rear indices in the new array frontIndex = 0; backIndex = sizeVar -1; // Deallocate the memory // of previous array delete[] arr; arr = temp; } // If size is zero if (empty()) { frontIndex = backIndex = 0; arr[backIndex] = x; sizeVar++; return; } // Increment the backIndex backIndex = (backIndex + 1) % capacityVar; arr[backIndex] = x; sizeVar++; return;}// Function to pop an element from// front end of the queuetemplate <class X>void Queue<X>::pop(){ // If queue is empty if (empty()) { cout << "Queue underflow" << endl; abort(); } // If there is only one character if (frontIndex == backIndex) { // Mark Queue as empty // and decrement sizeVar frontIndex = backIndex = -1; sizeVar--; return; } // Increment frontIndex cyclically // using modulo arithmetic frontIndex = (frontIndex + 1) % capacityVar; sizeVar--; return;}// Driver Codeint main(){ // Queue initialization Queue<int> q; // Iterate the range [1, 100] for (int i = 1; i < 5; i++) q.push(i); // Print the current capacity cout << "Current capacity " << q.capacity() << endl; // Print current size cout << "Current size " << q.size() << endl; // Print front elements of queue cout << "Front element " << q.front() << endl; // Print last element of the queue cout << "Rear element " << q.back() << endl; cout << endl; cout << "Pop an element" << endl; // Pop an element from the queue q.pop(); cout << "Pop an element" << endl; // Pop an element from the queue q.pop(); cout << endl; // Print the current capacity cout << "Current capacity " << q.capacity() << endl; // Print current size cout << "Current size " << q.size() << endl; // Print front elements of queue cout << "Front element " << q.front() << endl; // Print last element of the queue cout << "Rear element " << q.back() << endl; cout << endl; cout << "Push element 5" << endl; cout << "Push element 6" << endl; q.push(5); q.push(6); cout << endl; // Print the current capacity cout << "Current capacity " << q.capacity() << endl; // Print current size cout << "Current size " << q.size() << endl; // Print front elements of queue cout << "Front element " << q.front() << endl; // Print last element of the queue cout << "Rear element " << q.back() << endl; cout << endl; cout << "Push element 7" << endl; q.push(7); cout << endl; // Print the current capacity cout << "Current capacity " << q.capacity() << endl; // Print current size cout << "Current size " << q.size() << endl; // Print front elements of queue cout << "Front element " << q.front() << endl; // Print last element of the queue cout << "Rear element " << q.back() << endl; return 0;} |
Output:
Current capacity 128 Current size 99 Front element 1 Rear element 99 Pop an element Pop an element Current capacity 128 Current size 97 Front element 3 Rear element 99
Time Complexity: O(N)
Auxiliary Space: O(N)
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