Deque or Double Ended Queue is a generalized version of Queue data structure that allows insert and delete at both ends. In previous post Implementation of Deque using circular array has been discussed. Now in this post we see how we implement Deque using Doubly Linked List.
Operations on Deque :
Mainly the following four basic operations are performed on queue :
insertFront() : Adds an item at the front of Deque. insertRear() : Adds an item at the rear of Deque. deleteFront() : Deletes an item from front of Deque. deleteRear() : Deletes an item from rear of Deque.
In addition to above operations, following operations are also supported :
getFront() : Gets the front item from queue. getRear() : Gets the last item from queue. isEmpty() : Checks whether Deque is empty or not. size() : Gets number of elements in Deque. erase() : Deletes all the elements from Deque.
Doubly Linked List Representation of Deque :
For implementing deque, we need to keep track of two pointers, front and rear. We enqueue (push) an item at the rear or the front end of deque and dequeue(pop) an item from both rear and front end.
Working :
Declare two pointers front and rear of type Node, where Node represents the structure of a node of a doubly linked list. Initialize both of them with value NULL.
Insertion at Front end :
1. Allocate space for a newNode of doubly linked list. 2. IF newNode == NULL, then 3. print "Overflow" 4. ELSE 5. IF front == NULL, then 6. rear = front = newNode 7. ELSE 8. newNode->next = front 9. front->prev = newNode 10. front = newNode
Insertion at Rear end :
1. Allocate space for a newNode of doubly linked list. 2. IF newNode == NULL, then 3. print "Overflow" 4. ELSE 5. IF rear == NULL, then 6. front = rear = newNode 7. ELSE 8. newNode->prev = rear 9. rear->next = newNode 10. rear = newNode
Deletion from Front end :
1. IF front == NULL 2. print "Underflow" 3. ELSE 4. Initialize temp = front 5. front = front->next 6. IF front == NULL 7. rear = NULL 8. ELSE 9. front->prev = NULL 10 Deallocate space for temp
Deletion from Rear end :
1. IF front == NULL 2. print "Underflow" 3. ELSE 4. Initialize temp = rear 5. rear = rear->prev 6. IF rear == NULL 7. front = NULL 8. ELSE 9. rear->next = NULL 10 Deallocate space for temp
Implementation:
CPP
// C++ implementation of Deque using // doubly linked list #include <bits/stdc++.h> using namespace std; // Node of a doubly linked list struct Node { int data; Node *prev, *next; // Function to get a new node static Node* getnode(int data) { Node* newNode = (Node*)malloc(sizeof(Node)); newNode->data = data; newNode->prev = newNode->next = NULL; return newNode; } }; // A structure to represent a deque class Deque { Node* front; Node* rear; int Size; public: Deque() { front = rear = NULL; Size = 0; } // Operations on Deque void insertFront(int data); void insertRear(int data); void deleteFront(); void deleteRear(); int getFront(); int getRear(); int size(); bool isEmpty(); void erase(); }; // Function to check whether deque // is empty or not bool Deque::isEmpty() { return (front == NULL); } // Function to return the number of // elements in the deque int Deque::size() { return Size; } // Function to insert an element // at the front end void Deque::insertFront(int data) { Node* newNode = Node::getnode(data); // If true then new element cannot be added // and it is an 'Overflow' condition if (newNode == NULL) cout << "OverFlow\n"; else { // If deque is empty if (front == NULL) rear = front = newNode; // Inserts node at the front end else { newNode->next = front; front->prev = newNode; front = newNode; } // Increments count of elements by 1 Size++; } } // Function to insert an element // at the rear end void Deque::insertRear(int data) { Node* newNode = Node::getnode(data); // If true then new element cannot be added // and it is an 'Overflow' condition if (newNode == NULL) cout << "OverFlow\n"; else { // If deque is empty if (rear == NULL) front = rear = newNode; // Inserts node at the rear end else { newNode->prev = rear; rear->next = newNode; rear = newNode; } Size++; } } // Function to delete the element // from the front end void Deque::deleteFront() { // If deque is empty then // 'Underflow' condition if (isEmpty()) cout << "UnderFlow\n"; // Deletes the node from the front end and makes // the adjustment in the links else { Node* temp = front; front = front->next; // If only one element was present if (front == NULL) rear = NULL; else front->prev = NULL; free(temp); // Decrements count of elements by 1 Size--; } } // Function to delete the element // from the rear end void Deque::deleteRear() { // If deque is empty then // 'Underflow' condition if (isEmpty()) cout << "UnderFlow\n"; // Deletes the node from the rear end and makes // the adjustment in the links else { Node* temp = rear; rear = rear->prev; // If only one element was present if (rear == NULL) front = NULL; else rear->next = NULL; free(temp); // Decrements count of elements by 1 Size--; } } // Function to return the element // at the front end int Deque::getFront() { // If deque is empty, then returns // garbage value if (isEmpty()) return -1; return front->data; } // Function to return the element // at the rear end int Deque::getRear() { // If deque is empty, then returns // garbage value if (isEmpty()) return -1; return rear->data; } // Function to delete all the elements // from Deque void Deque::erase() { rear = NULL; while (front != NULL) { Node* temp = front; front = front->next; free(temp); } Size = 0; } // Driver program to test above int main() { Deque dq; cout << "Insert element '5' at rear end\n"; dq.insertRear(5); cout << "Insert element '10' at rear end\n"; dq.insertRear(10); cout << "Rear end element: " << dq.getRear() << endl; dq.deleteRear(); cout << "After deleting rear element new rear" << " is: " << dq.getRear() << endl; cout << "Inserting element '15' at front end \n"; dq.insertFront(15); cout << "Front end element: " << dq.getFront() << endl; cout << "Number of elements in Deque: " << dq.size() << endl; dq.deleteFront(); cout << "After deleting front element new " << "front is: " << dq.getFront() << endl; return 0; } |
Java
// Java implementation of Deque using // doubly linked list import java.util.*; class GFG { // Node of a doubly linked list static class Node { int data; Node prev, next; // Function to get a new node static Node getnode(int data) { Node newNode = new Node(); newNode.data = data; newNode.prev = newNode.next = null; return newNode; } }; // A structure to represent a deque static class Deque { Node front; Node rear; int Size; Deque() { front = rear = null; Size = 0; } // Function to check whether deque // is empty or not boolean isEmpty() { return (front == null); } // Function to return the number of // elements in the deque int size() { return Size; } // Function to insert an element // at the front end void insertFront(int data) { Node newNode = Node.getnode(data); // If true then new element cannot be added // and it is an 'Overflow' condition if (newNode == null) System.out.print("OverFlow\n"); else { // If deque is empty if (front == null) rear = front = newNode; // Inserts node at the front end else { newNode.next = front; front.prev = newNode; front = newNode; } // Increments count of elements by 1 Size++; } } // Function to insert an element // at the rear end void insertRear(int data) { Node newNode = Node.getnode(data); // If true then new element cannot be added // and it is an 'Overflow' condition if (newNode == null) System.out.print("OverFlow\n"); else { // If deque is empty if (rear == null) front = rear = newNode; // Inserts node at the rear end else { newNode.prev = rear; rear.next = newNode; rear = newNode; } Size++; } } // Function to delete the element // from the front end void deleteFront() { // If deque is empty then // 'Underflow' condition if (isEmpty()) System.out.print("UnderFlow\n"); // Deletes the node from the front end and makes // the adjustment in the links else { Node temp = front; front = front.next; // If only one element was present if (front == null) rear = null; else front.prev = null; // Decrements count of elements by 1 Size--; } } // Function to delete the element // from the rear end void deleteRear() { // If deque is empty then // 'Underflow' condition if (isEmpty()) System.out.print("UnderFlow\n"); // Deletes the node from the rear end and makes // the adjustment in the links else { Node temp = rear; rear = rear.prev; // If only one element was present if (rear == null) front = null; else rear.next = null; // Decrements count of elements by 1 Size--; } } // Function to return the element // at the front end int getFront() { // If deque is empty, then returns // garbage value if (isEmpty()) return -1; return front.data; } // Function to return the element // at the rear end int getRear() { // If deque is empty, then returns // garbage value if (isEmpty()) return -1; return rear.data; } // Function to delete all the elements // from Deque void erase() { rear = null; while (front != null) { Node temp = front; front = front.next; } Size = 0; } } // Driver program to test above public static void main(String[] args) { Deque dq = new Deque(); System.out.print( "Insert element '5' at rear end\n"); dq.insertRear(5); System.out.print( "Insert element '10' at rear end\n"); dq.insertRear(10); System.out.print("Rear end element: " + dq.getRear() + "\n"); dq.deleteRear(); System.out.print( "After deleting rear element new rear" + " is: " + dq.getRear() + "\n"); System.out.print( "Inserting element '15' at front end \n"); dq.insertFront(15); System.out.print( "Front end element: " + dq.getFront() + "\n"); System.out.print("Number of elements in Deque: " + dq.size() + "\n"); dq.deleteFront(); System.out.print("After deleting front element new " + "front is: " + dq.getFront() + "\n"); } } // This code is contributed by gauravrajput1 |
Python3
class GFG: # Node of a doubly linked list class Node: data = 0 prev = None next = None # Function to get a new node @staticmethod def getnode(data): newNode = GFG.Node() newNode.data = data newNode.prev = None newNode.next = None return newNode # A structure to represent a deque class Deque: front = None rear = None Size = 0 def __init__(self): self.front = None self.rear = None self.Size = 0 # Function to check whether deque # is empty or not def isEmpty(self): return (self.front == None) # Function to return the number of # elements in the deque def size(self): return self.Size # Function to insert an element # at the front end def insertFront(self, data): newNode = GFG.Node.getnode(data) # If true then new element cannot be added # and it is an 'Overflow' condition if (newNode == None): print("OverFlow\n", end="") else: # If deque is empty if (self.front == None): self.rear = newNode self.front = newNode else: newNode.next = self.front self.front.prev = newNode self.front = newNode # Increments count of elements by 1 self.Size += 1 # Function to insert an element # at the rear end def insertRear(self, data): newNode = GFG.Node.getnode(data) # If true then new element cannot be added # and it is an 'Overflow' condition if (newNode == None): print("OverFlow\n", end="") else: # If deque is empty if (self.rear == None): self.front = newNode self.rear = newNode else: newNode.prev = self.rear self.rear.next = newNode self.rear = newNode self.Size += 1 # Function to delete the element # from the front end def deleteFront(self): # If deque is empty then # 'Underflow' condition if (self.isEmpty()): print("UnderFlow\n", end="") else: temp = self.front self.front = self.front.next # If only one element was present if (self.front == None): self.rear = None else: self.front.prev = None # Decrements count of elements by 1 self.Size -= 1 # Function to delete the element # from the rear end def deleteRear(self): # If deque is empty then # 'Underflow' condition if (self.isEmpty()): print("UnderFlow\n", end="") else: temp = self.rear self.rear = self.rear.prev # If only one element was present if (self.rear == None): self.front = None else: self.rear.next = None # Decrements count of elements by 1 self.Size -= 1 # Function to return the element # at the front end def getFront(self): # If deque is empty, then returns # garbage value if (self.isEmpty()): return -1 return self.front.data # Function to return the element # at the rear end def getRear(self): # If deque is empty, then returns # garbage value if (self.isEmpty()): return -1 return self.rear.data # Function to delete all the elements # from Deque def erase(self): self.rear = None while (self.front != None): temp = self.front self.front = self.front.next self.Size = 0 # Driver program to test above @staticmethod def main(args): dq = GFG.Deque() print("Insert element \'5\' at rear end\n", end="") dq.insertRear(5) print("Insert element \'10\' at rear end\n", end="") dq.insertRear(10) print("Rear end element: " + str(dq.getRear()) + "\n", end="") dq.deleteRear() print("After deleting rear element new rear" + " is: " + str(dq.getRear()) + "\n", end="") print("Inserting element \'15\' at front end \n", end="") dq.insertFront(15) print("Front end element: " + str(dq.getFront()) + "\n", end="") print("Number of elements in Deque: " + str(dq.size()) + "\n", end="") dq.deleteFront() print("After deleting front element new " + "front is: " + str(dq.getFront()) + "\n", end="") if __name__ == "__main__": GFG.main([]) # This code is contributed by aadityaburujwale. |
Javascript
// Javascript implementation of Deque using // Node of a doubly linked list class Node { data = 0; prev = null; next = null; // Function to get a new node static getnode(data) { const newNode = new Node(); newNode.data = data; newNode.prev = null; newNode.next = null; return newNode; } } // A structure to represent a deque class Deque { front = null; rear = null; size = 0; constructor() { this.front = null; this.rear = null; this.size = 0; } // Function to check whether deque // is empty or not isEmpty() { return this.front === null; } // Function to return the number of // elements in the deque size() { return this.size; } // Function to insert an element // at the front end insertFront(data) { const newNode = Node.getnode(data); // If true then new element cannot be added // and it is an 'Overflow' condition if (newNode === null) { console.log("OverFlow\n"); } else { // If deque is empty if (this.front === null) { this.rear = newNode; this.front = newNode; } else { newNode.next = this.front; this.front.prev = newNode; this.front = newNode; } // Increments count of elements by 1 this.size += 1; } } // Function to insert an element // at the rear end insertRear(data) { const newNode = Node.getnode(data); // If true then new element cannot be added // and it is an 'Overflow' condition if (newNode === null) { console.log("OverFlow\n"); } else { // If deque is empty if (this.rear === null) { this.front = newNode; this.rear = newNode; } else { newNode.prev = this.rear; this.rear.next = newNode; this.rear = newNode; } this.size += 1; } } // Function to delete the element // from the front end deleteFront() { // If deque is empty then // 'Underflow' condition if (this.isEmpty()) { console.log("UnderFlow\n"); } else { const temp = this.front; this.front = this.front.next; // If only one element was present if (this.front === null) { this.rear = null; } else { this.front.prev = null; } // Decrements count of elements by 1 this.size -= 1; } } deleteRear() { // If deque is empty then // 'Underflow' condition if (this.isEmpty()) { console.log("UnderFlow\n"); } else { const temp = this.rear; this.rear = this.rear.prev; // If only one element was present if (this.rear === null) { this.front = null; } else { this.rear.next = null; } // Decrements count of elements by 1 this.size -= 1; } } // Function to return the element // at the front end getFront() { // If deque is empty, then returns // garbage value if (this.isEmpty()) { return -1; } return this.front.data; } // Function to return the element // at the rear end getRear() { // If deque is empty, then returns // garbage value if (this.isEmpty()) { return -1; } return this.rear.data; } // Function to delete all the elements // from Deque erase() { this.rear = null; while (this.front !== null) { const temp = this.front; this.front = this.front.next; } this.size = 0; } } // Driver program to test the Deque class function main() { // Create a Deque object const dq = new Deque(); console.log("Insert element '5' at rear end"); dq.insertRear(5); console.log("Insert element '10' at rear end"); dq.insertRear(10); console.log(`Rear end element: ${dq.getRear()}`); dq.deleteRear(); console.log(`After deleting rear element new rear is: ${dq.getRear()}`); console.log("Inserting element '15' at front end"); dq.insertFront(15); console.log(`Front end element: ${dq.getFront()}`); console.log(`Number of elements in Deque: ${dq.size}`); dq.deleteFront(); console.log(`After deleting front element new front is: ${dq.getFront()}`); } // Call the main function main(); |
Output
Insert element '5' at rear end Insert element '10' at rear end Rear end element: 10 After deleting rear element new rear is: 5 Inserting element '15' at front end Front end element: 15 Number of elements in Deque: 2 After deleting front element new front is: 5
Complexity Analysis:
- Time Complexity : Time complexity of operations like insertFront(), insertRear(), deleteFront(), deleteRear() is O(1). The Time Complexity of erase() is O(n).
- Auxiliary space: O(1)
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