The task is to implement a dynamic Deque using templates class and a circular array, having the following functionalities:
- front(): Get the front item from the deque.
- back(): Get the last item from the deque.
- push_back(X): Push X at the end of the deque.
- push_front(X): Push X at the start of the deque.
- pop_front(): Delete an element from the start of the deque.
- pop_back(): Delete an element from the end of the deque
- empty(): Checks whether deque is empty or not
- capacity(): Current maximum number of elements deque can store
- size(): Number of elements in the deque
Below is the step by step illustration:
- Initially, the deque is empty
- Insert 1 to the back of deque
- Insert elements 2, 3 to the back of deque
- Insert 4 to the front of deque
- Insert 5 to the back of deque
- Pop 2 elements from front and 2 elements from the back of deque
- Pop 1 element from the front of deque
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 capacityVar, and an array say arr[] to implement the deque.
- Define a function say capacity() to find the size of the current array used and return the value of the variable, capacityVar.
- Define a function say size() to find the count of elements in the deque and return the value of the variable, sizeVar.
- Define a function say full() to find if the deque is full or not and return true if sizeVar is equal to capacityVar. Otherwise, return false.
- Define a function say empty() to find if the deque is empty or not and return true if frontIndex and backIndex are equal to -1. Otherwise, return false.
- Define a function say Front() to print the front element of the deque. If deque is not empty(), print the element of arr[frontIndex].
- Define a function say Back() to print the last element of the deque. If deque is not empty(), print the element of arr[BackIndex].
- Define a function say push_back(X) to insert an element at the end of the deque:
- If the deque is full, then double the size of the current array and copy the elements of the previous array into the new array.
- If deque 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) %capacityVar and then assign X to arr[backIndex] and increment sizeVar by one.
- Define a function say push_front(X) to insert an element at the start of the deque:
- If the deque is full, then double the size of the current array and copy the elements of the previous array into the new array.
- If deque 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 frontIndex as frontIndex = (frontIndex-1 + capacityVar)%capacityVar and then assign X to arr[frontIndex] and increment sizeVar by one.
- Define a function say pop_front() to delete an element at the front of the deque:
- If the deque 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)%capacityVar and decrement sizeVar by one.
- Define a function say pop_back() to delete an element at the front of the deque:
- If the deque 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 backIndex as backIndex = (backndex-1 + capacityVar) %capacityVar 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 of the dequetemplate <class X>class Deque {private: // Stores the frontIndex int frontIndex; // Stores the backIndex int backIndex; // Stores the array X* arr; // Stores the size of deque int sizeVar; // Stores the size of array int capacityVar = 4;public: // Deque class constructor Deque() { arr = new X[capacityVar]; frontIndex = backIndex = -1; sizeVar = 0; } // Function methods bool empty(); bool full(); void push_back(X x); void push_front(X x); void pop_front(); void pop_back(); X front(); X back(); int capacity(); int size();};// Function to find the capacity of the dequetemplate <class X>int Deque<X>::capacity(){ return capacityVar;}// Function to find the number of elements// present in dequetemplate <class X>int Deque<X>::size() { return sizeVar; }// Function to check if deque is empty or nottemplate <class X>bool Deque<X>::empty(){ if (frontIndex == -1 && backIndex == -1) return true; else return false;}// Function to check if deque is full or nottemplate <class X>bool Deque<X>::full(){ if (sizeVar == capacityVar) return true; else return false;}// Function to find the front element of the dequetemplate <class X>X Deque<X>::front(){ // If deque is empty if (empty()) { cout << "Deque underflow" << endl; abort(); } return arr[frontIndex];}// Function to find the last element of the dequetemplate <class X>X Deque<X>::back(){ // If deque is empty if (empty()) { cout << "Deque underflow" << endl; abort(); } return arr[backIndex];}// Function to insert the element// to the back of the dequetemplate <class X>void Deque<X>::push_back(X x){ if (full()) { // If the deque 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 int i = frontIndex; int j = 0; while (i != backIndex) { temp[j] = arr[i]; i = (i + 1) % sizeVar; j++; } temp[j] = arr[i]; 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 back index cyclically backIndex = (backIndex + 1) % capacityVar; arr[backIndex] = x; sizeVar++; return;}// Function to insert the element// to the front of the dequetemplate <class X>void Deque<X>::push_front(X x){ if (full()) { // If the deque 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 int i = frontIndex; int j = 0; while (i != backIndex) { temp[j] = arr[i]; i = (i + 1) % sizeVar; j++; } temp[j] = arr[i]; 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; } // Decrement front index cyclically frontIndex = (frontIndex - 1 + capacityVar) % capacityVar; arr[frontIndex] = x; sizeVar++; return;}// Function to delete the element// from the front of the dequetemplate <class X>void Deque<X>::pop_front(){ // If deque is empty if (empty()) { cout << "Deque underflow" << endl; abort(); } // If there is only one character if (frontIndex == backIndex) { // Mark deque as empty // and decrement sizeVar frontIndex = backIndex = -1; sizeVar--; return; } // Increment frontIndex cyclically frontIndex = (frontIndex + 1) % capacityVar; sizeVar--; return;}// Function to delete the element// from the back of the dequetemplate <class X>void Deque<X>::pop_back(){ // If deque is empty if (empty()) { cout << "Deque underflow" << endl; abort(); } // If there is only one character if (frontIndex == backIndex) { // Mark deque as empty // and decrement sizeVar frontIndex = backIndex = -1; sizeVar--; return; } // Decrement backIndex cyclically backIndex = (backIndex - 1 + capacityVar) % capacityVar; sizeVar--; return;}// Driver Codeint main(){ // Deque initialization Deque<int> q; // Iterate range [1, 100], // push even numbers at the back // and push odd numbers at the front for (int i = 1; i < 10; i++) if (i % 2 == 0) q.push_back(i); else q.push_front(i); // Print the current capacity cout << "Current capacity " << q.capacity() << endl; // Print the current size cout << "Current size " << q.size() << endl; // Print front elements of deque cout << "Front element " << q.front() << endl; // Print last element of the deque cout << "Rear element " << q.back() << endl; cout << endl; cout << "Pop an element from front" << endl; // Pop an element from the front of deque q.pop_front(); cout << "Pop an element from back" << endl; // Pop an element from the back of deque q.pop_back(); 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 deque cout << "Front element " << q.front() << endl; // Print last element of the deque cout << "Rear element " << q.back() << endl; return 0;} |
Output
Current capacity 16 Current size 9 Front element 9 Rear element 8 Pop an element from front Pop an element from back Current capacity 16 Current size 7 Front element 7 Rear element 6
Time Complexity: O(N)
Auxiliary Space: O(N)
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