Implement Stack and Queue using Deque Last Updated : 17 Apr, 2024 Summarize Suggest changes Share Like Article Like Report Deque also known as double ended queue, as name suggests is a special kind of queue in which insertions and deletions can be done at the last as well as at the beginning. A link-list representation of deque is such that each node points to the next node as well as the previous node. So that insertion and deletions take constant time at both the beginning and the last. Now, deque can be used to implement a stack and queue. One simply needs to understand how deque can made to work as a stack or a queue. The functions of deque to tweak them to work as stack and queue are list below. Examples: Stack Input : Stack : 1 2 3 Push(4)Output : Stack : 1 2 3 4Input : Stack : 1 2 3 Pop()Output : Stack : 1 2Examples: Queue Input: Queue : 1 2 3 Enqueue(4)Output: Queue : 1 2 3 4Input: Queue : 1 2 3 Dequeue()Output: Queue : 2 3Implementation: Java // Java program to implement stack and // queue using Deque import java.lang.*; class GFG { // Class for a node of deque static class DQueNode { int value; DQueNode next; DQueNode prev; } // Implementation of deque class static class deque { // Pointers to head and tail of deque private DQueNode head; private DQueNode tail; // Constructor public deque() { head = tail = null; } // If list is empty boolean isEmpty() { if (head == null) return true; return false; } // count the number of nodes in list int size() { // If list is not empty if (!isEmpty()) { DQueNode temp = head; int len = 0; while (temp != null) { len++; temp = temp.next; } return len; } return 0; } // Insert at the first position void insert_first(int element) { // Allocating node of DQueNode type DQueNode temp = new DQueNode(); temp.value = element; // If the element is first element if (head == null) { head = tail = temp; temp.next = temp.prev = null; } else { head.prev = temp; temp.next = head; temp.prev = null; head = temp; } } // Insert at last position of deque void insert_last(int element) { // Allocating node of DQueNode type DQueNode temp = new DQueNode(); temp.value = element; // If element is the first element if (head == null) { head = tail = temp; temp.next = temp.prev = null; } else { tail.next = temp; temp.next = null; temp.prev = tail; tail = temp; } } // Remove element at the first position public void remove_first() { // If list is not empty if (!isEmpty()) { // If there is only one node if (head == tail) { head = tail = null; return; } else { head = head.next; head.prev = null; } } else { System.out.println("List is Empty"); } } // Remove element at the last position void remove_last() { // If list is not empty if (!isEmpty()) { DQueNode temp = tail; tail = tail.prev; if (tail != null) { tail.next = null; } return; } System.out.print("List is Empty"); } // Displays the elements in deque void display() { // If list is not empty if (!isEmpty()) { DQueNode temp = head; while (temp != null) { System.out.print(temp.value + " "); temp = temp.next; } return; } System.out.print("List is Empty"); } } // Class to implement stack using Deque static class Stack { deque d = new deque(); // push to push element at top of stack // using insert at last function of deque public void push(int element) { d.insert_last(element); } // Returns size public int size() { return d.size(); } // pop to remove element at top of stack // using remove at last function of deque public void pop() { d.remove_last(); } // Display public void display() { d.display(); } } // Class to implement queue using deque static class Queue { deque d = new deque(); // enqueue to insert element at last // using insert at last function of deque public void enqueue(int element) { d.insert_last(element); } // dequeue to remove element from first // using remove at first function of deque public void dequeue() { d.remove_first(); } // display public void display() { d.display(); } // size public int size() { return d.size(); } } // Driver Code public static void main(String[] args) { // Object of Stack Stack stk = new Stack(); // push 7 and 8 at top of stack stk.push(7); stk.push(8); System.out.print("Stack: "); stk.display(); // For new line System.out.println(); // pop an element stk.pop(); System.out.print("Stack: "); stk.display(); // For new line System.out.println(); // Object of Queue Queue que = new Queue(); // Insert 12 and 13 in queue que.enqueue(12); que.enqueue(13); System.out.print("Queue: "); que.display(); // New line System.out.println(); // Delete an element from queue que.dequeue(); System.out.print("Queue: "); que.display(); // New line System.out.println(); System.out.println("Size of stack is " + stk.size()); System.out.println("Size of queue is " + que.size()); } } // This code is contributed by sujitmeshram // This code is modified by Susobhan Akhuli // This code is modified by K.Harichandana Python3 class node: def __init__(self,val): self.val = val self.prev = None self.next = None class Deque: def __init__(self): self.head = self.tail = None def isEmpty(self): if (self.head == None): return True return False def insert_first(self,element): newP = node(element) if self.head == None: self.head = self.tail = newP return newP.next = self.head self.head.prev = newP self.head = newP def insert_last(self,element): newP = node(element) if self.head == None: self.head = self.tail = newP return newP.prev = self.tail self.tail.next = newP self.tail = newP def size(self): curr = self.head len = 0 while curr != None: len += 1 curr = curr.next return len def remove_first(self): if self.isEmpty(): print('List is Empty') return self.head = self.head.next if self.head != None: self.head.prev = None def remove_last(self): if self.isEmpty(): print('List is Empty') return self.tail = self.tail.prev if self.tail != None: self.tail.next = None def display(self): if self.isEmpty(): print('List is Empty') return curr = self.head while curr != None: print(curr.val,end = ' ') curr = curr.next print() class Stack: def __init__(self): self.stack = Deque() def push(self,element): self.stack.insert_last(element) def pop(self): self.stack.remove_last() def size(self): return self.stack.size() def display(self): self.stack.display() class Queue: def __init__(self): self.que = Deque() def enqueue(self,element): self.que.insert_last(element) def dequeue(self): self.que.remove_first() def size(self): return self.que.size() def display(self): self.que.display() stk = Stack() # push 7 and 8 at top of stack stk.push(7) stk.push(8) print("Stack: ") stk.display() # pop an element stk.pop() print("Stack: ") stk.display() # Object of Queue que = Queue() # Insert 12 and 13 in queue que.enqueue(12) que.enqueue(13) print("Queue: ") que.display() # Delete an element from queue que.dequeue() print("Queue: ") que.display() print("Size of stack is ",stk.size()) print("Size of queue is ", que.size()) C# // C# program to implement stack and // queue using Deque using System; class GFG { // Class for a node of deque public class DQueNode { public int value; public DQueNode next; public DQueNode prev; } // Implementation of deque class public class deque { // Pointers to head and tail of deque private DQueNode head; private DQueNode tail; // Constructor public deque() { head = tail = null; } // If list is empty public bool isEmpty() { if (head == null) return true; return false; } // count the number of nodes in list public int size() { // If list is not empty if (!isEmpty()) { DQueNode temp = head; int len = 0; while (temp != null) { len++; temp = temp.next; } return len; } return 0; } // Insert at the first position public void insert_first(int element) { // Allocating node of DQueNode type DQueNode temp = new DQueNode(); temp.value = element; // If the element is first element if (head == null) { head = tail = temp; temp.next = temp.prev = null; } else { head.prev = temp; temp.next = head; temp.prev = null; head = temp; } } // Insert at last position of deque public void insert_last(int element) { // Allocating node of DQueNode type DQueNode temp = new DQueNode(); temp.value = element; // If element is the first element if (head == null) { head = tail = temp; temp.next = temp.prev = null; } else { tail.next = temp; temp.next = null; temp.prev = tail; tail = temp; } } // Remove element at the first position public void remove_first() { // If list is not empty if (!isEmpty()) { head = head.next; head.prev = null; return; } Console.Write("List is Empty"); } // Remove element at the last position public void remove_last() { // If list is not empty if (!isEmpty()) { tail = tail.prev; tail.next = null; return; } Console.Write("List is Empty"); } // Displays the elements in deque public void display() { // If list is not empty if (!isEmpty()) { DQueNode temp = head; while (temp != null) { Console.Write(temp.value + " "); temp = temp.next; } return; } Console.Write("List is Empty"); } } // Class to implement stack using Deque public class Stack { deque d = new deque(); // push to push element at top of stack // using insert at last function of deque public void push(int element) { d.insert_last(element); } // Returns size public int size() { return d.size(); } // pop to remove element at top of stack // using remove at last function of deque public void pop() { d.remove_last(); } // Display public void display() { d.display(); } } // Class to implement queue using deque class Queue { deque d = new deque(); // enqueue to insert element at last // using insert at last function of deque public void enqueue(int element) { d.insert_last(element); } // dequeue to remove element from first // using remove at first function of deque public void dequeue() { d.remove_first(); } // display public void display() { d.display(); } // size public int size() { return d.size(); } } // Driver Code public static void Main(String[] args) { // Object of Stack Stack stk = new Stack(); // push 7 and 8 at top of stack stk.push(7); stk.push(8); Console.Write("Stack: "); stk.display(); // For new line Console.WriteLine(); // pop an element stk.pop(); Console.Write("Stack: "); stk.display(); // For new line Console.WriteLine(); // Object of Queue Queue que = new Queue(); // Insert 12 and 13 in queue que.enqueue(12); que.enqueue(13); Console.Write("Queue: "); que.display(); // New line Console.WriteLine(); // Delete an element from queue que.dequeue(); Console.Write("Queue: "); que.display(); // New line Console.WriteLine(); Console.WriteLine("Size of stack is " + stk.size()); Console.WriteLine("Size of queue is " + que.size()); } } // This code contributed by gauravrajput1 JavaScript <script> // Javascript program to implement stack and // queue using Deque // Class for a node of deque class DQueNode { constructor() { this.value = 0; this.next = null; this.prev = null; } } // Implementation of deque class class deque { // Constructor constructor() { this.head = this.tail=null; } // If list is empty isEmpty() { if (this.head == null) return true; return false; } // count the number of nodes in list size() { // If list is not empty if (!this.isEmpty()) { let temp = this.head; let len = 0; while (temp != null) { len++; temp = temp.next; } return len; } return 0; } // Insert at the first position insert_first(element) { // Allocating node of DQueNode type let temp = new DQueNode(); temp.value = element; // If the element is first element if (this.head == null) { this.head = this.tail = temp; temp.next = temp.prev = null; } else { this.head.prev = temp; temp.next = this.head; temp.prev = null; this.head = temp; } } // Insert at last position of deque insert_last(element) { // Allocating node of DQueNode type let temp = new DQueNode(); temp.value = element; // If element is the first element if (this.head == null) { this.head = this.tail = temp; temp.next = temp.prev = null; } else { this.tail.next = temp; temp.next = null; temp.prev = this.tail; this.tail = temp; } } // Remove element at the first position remove_first() { // If list is not empty if (!this.isEmpty()) { let temp = this.head; this.head = this.head.next; this.head.prev = null; return; } document.write("List is Empty"); } // Remove element at the last position remove_last() { // If list is not empty if (!this.isEmpty()) { let temp = this.tail; this.tail = this.tail.prev; this.tail.next = null; return; } document.write("List is Empty"); } // Displays the elements in deque display() { // If list is not empty if (!this.isEmpty()) { let temp = this.head; while (temp != null) { document.write(temp.value + " "); temp = temp.next; } return; } document.write("List is Empty"); } } // Class to implement stack using Deque class Stack { constructor() { this.d= new deque(); } // push to push element at top of stack // using insert at last function of deque push(element) { this.d.insert_last(element); } // Returns size size() { return this.d.size(); } // pop to remove element at top of stack // using remove at last function of deque pop() { this.d.remove_last(); } // Display display() { this.d.display(); } } // Class to implement queue using deque class Queue { constructor() { this.d = new deque(); } // enqueue to insert element at last // using insert at last function of deque enqueue(element) { this.d.insert_last(element); } // dequeue to remove element from first // using remove at first function of deque dequeue() { this.d.remove_first(); } // display display() { this.d.display(); } // size size() { return this.d.size(); } } // Driver Code // Object of Stack let stk = new Stack(); // push 7 and 8 at top of stack stk.push(7); stk.push(8); document.write("Stack: "); stk.display(); // For new line document.write("<br>"); // pop an element stk.pop(); document.write("Stack: "); stk.display(); // For new line document.write("<br>"); // Object of Queue let que = new Queue(); // Insert 12 and 13 in queue que.enqueue(12); que.enqueue(13); document.write("Queue: "); que.display(); // New line document.write("<br>"); // Delete an element from queue que.dequeue(); document.write("Queue: "); que.display(); // New line document.write("<br>"); document.write("Size of stack is " + stk.size()+"<br>"); document.write("Size of queue is " + que.size()+"<br>"); // This code is contributed by patel2127 </script> C++14 // C++ Program to implement stack and queue using Deque #include <bits/stdc++.h> using namespace std; // structure for a node of deque struct DQueNode { int value; DQueNode* next; DQueNode* prev; }; // Implementation of deque class class Deque { private: // pointers to head and tail of deque DQueNode* head; DQueNode* tail; public: // constructor Deque() { head = tail = NULL; } // if list is empty bool isEmpty() { if (head == NULL) return true; return false; } // count the number of nodes in list int size() { // if list is not empty if (!isEmpty()) { DQueNode* temp = head; int len = 0; while (temp != NULL) { len++; temp = temp->next; } return len; } return 0; } // insert at the first position void insert_first(int element) { // allocating node of DQueNode type DQueNode* temp = new DQueNode[sizeof(DQueNode)]; temp->value = element; // if the element is first element if (head == NULL) { head = tail = temp; temp->next = temp->prev = NULL; } else { head->prev = temp; temp->next = head; temp->prev = NULL; head = temp; } } // insert at last position of deque void insert_last(int element) { // allocating node of DQueNode type DQueNode* temp = new DQueNode[sizeof(DQueNode)]; temp->value = element; // if element is the first element if (head == NULL) { head = tail = temp; temp->next = temp->prev = NULL; } else { tail->next = temp; temp->next = NULL; temp->prev = tail; tail = temp; } } // remove element at the first position void remove_first() { // if list is not empty if (!isEmpty()) { DQueNode* temp = head; head = head->next; if(head) head->prev = NULL; delete temp; if(head == NULL) tail = NULL; return; } cout << "List is Empty" << endl; } // remove element at the last position void remove_last() { // if list is not empty if (!isEmpty()) { DQueNode* temp = tail; tail = tail->prev; if(tail) tail->next = NULL; delete temp; if(tail == NULL) head = NULL; return; } cout << "List is Empty" << endl; } // displays the elements in deque void display() { // if list is not empty if (!isEmpty()) { DQueNode* temp = head; while (temp != NULL) { cout << temp->value << " "; temp = temp->next; } cout << endl; return; } cout << "List is Empty" << endl; } }; // Class to implement stack using Deque class Stack : public Deque { public: // push to push element at top of stack // using insert at last function of deque void push(int element) { insert_last(element); } // pop to remove element at top of stack // using remove at last function of deque void pop() { remove_last(); } }; // class to implement queue using deque class Queue : public Deque { public: // enqueue to insert element at last // using insert at last function of deque void enqueue(int element) { insert_last(element); } // dequeue to remove element from first // using remove at first function of deque void dequeue() { remove_first(); } }; // Driver Code int main() { // object of Stack Stack stk; // push 7 and 8 at top of stack stk.push(7); stk.push(8); cout << "Stack: "; stk.display(); // pop an element stk.pop(); cout << "Stack: "; stk.display(); // object of Queue Queue que; // insert 12 and 13 in queue que.enqueue(12); que.enqueue(13); cout << "Queue: "; que.display(); // delete an element from queue que.dequeue(); cout << "Queue: "; que.display(); cout << "Size of Stack is " << stk.size() << endl; cout << "Size of Queue is " << que.size() << endl; return 0; } OutputStack: 7 8 Stack: 7 Queue: 12 13 Queue: 13 Size of Stack is 1 Size of Queue is 1 Time Complexity: O(n)Auxiliary Space: O(n) Advertise with us Next Article Infix to Postfix Expression S shubham_rana_77 Follow Similar Reads Stack Data Structure A Stack is a linear data structure that follows a particular order in which the operations are performed. 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If we use array implementation of the stack, then 8 min read The Stock Span ProblemThe stock span problem is a financial problem where we have a series of daily price quotes for a stock denoted by an array arr[] and the task is to calculate the span of the stock's price for all days. The span of the stock's price on ith day represents the maximum number of consecutive days leading 11 min read Next Greater Element (NGE) for every element in given ArrayGiven an array arr[] of integers, the task is to find the Next Greater Element for each element of the array in order of their appearance in the array. Note: The Next Greater Element for an element x is the first greater element on the right side of x in the array. Elements for which no greater elem 9 min read Next Greater Frequency ElementGiven an array arr[], for each element, find the nearest element to its right that has a higher frequency than the current element. If no such element exists, set the value to -1.Examples: Input: arr[] = [2, 1, 1, 3, 2, 1]Output: [1, -1, -1, 2, 1, -1] Explanation: Frequencies: 1 → 3 times, 2 → 2 tim 9 min read Maximum product of indexes of next greater on left and rightGiven an array arr[1..n], for each element at position i (1 <= i <= n), define the following:left(i) is the closest index j such that j < i and arr[j] > arr[i]. If no such j exists, then left(i) = 0.right(i) is the closest index k such that k > i and arr[k] > arr[i]. If no such k e 11 min read Iterative Tower of HanoiThe Tower of Hanoi is a mathematical puzzle with three poles and stacked disks of different sizes. The goal is to move all disks from the source pole to the destination pole using an auxiliary pole, following two rules:Only one disk can be moved at a time.A larger disk cannot be placed on a smaller 6 min read Sort a stack using a temporary stackGiven a stack of integers, sort it in ascending order using another temporary stack.Examples: Input: [34, 3, 31, 98, 92, 23]Output: [3, 23, 31, 34, 92, 98]Explanation: After Sorting the given array it would be look like as [3, 23, 31, 34, 92, 98]Input: [3, 5, 1, 4, 2, 8]Output: [1, 2, 3, 4, 5, 8] Ap 6 min read Reverse a stack without using extra space in O(n)Reverse a Stack without using recursion and extra space. Even the functional Stack is not allowed. Examples: Input : 1->2->3->4 Output : 4->3->2->1 Input : 6->5->4 Output : 4->5->6 We have discussed a way of reversing a stack in the below post.Reverse a Stack using Recu 6 min read Delete middle element of a stackGiven a stack with push(), pop(), and empty() operations, The task is to delete the middle element of it without using any additional data structure.Input: s = [10, 20, 30, 40, 50]Output: [50, 40, 20, 10]Explanation: The bottom-most element will be 10 and the top-most element will be 50. Middle elem 8 min read Check if a queue can be sorted into another queue using a stackGiven a Queue consisting of first n natural numbers (in random order). The task is to check whether the given Queue elements can be arranged in increasing order in another Queue using a stack. The operation allowed are: Push and pop elements from the stack Pop (Or Dequeue) from the given Queue. Push 9 min read Check if an array is stack sortableGiven an array arr[] of n distinct elements, where each element is between 1 and n (inclusive), determine if it is stack-sortable.Note: An array a[] is considered stack-sortable if it can be rearranged into a sorted array b[] using a temporary stack stk with the following operations:Remove the first 6 min read Largest Rectangular Area in a HistogramGiven a histogram represented by an array arr[], where each element of the array denotes the height of the bars in the histogram. All bars have the same width of 1 unit.Task is to find the largest rectangular area possible in a given histogram where the largest rectangle can be made of a number of c 15+ min read Maximum of minimums of every window size in a given arrayGiven an integer array arr[] of size n, the task is to find the maximum of the minimums for every window size in the given array, where the window size ranges from 1 to n.Example:Input: arr[] = [10, 20, 30]Output: [30, 20, 10]Explanation: First element in output indicates maximum of minimums of all 14 min read Index of closing bracket for a given opening bracket in an expressionGiven a string with brackets. If the start index of the open bracket is given, find the index of the closing bracket. Examples:Input : string = [ABC[23]][89] index = 0Output : 8The opening bracket at index 0 correspondsto closing bracket at index 8.The idea is to use Stack data structure. We travers 7 min read Maximum difference between nearest left and right smaller elementsGiven an array of integers, the task is to find the maximum absolute difference between the nearest left and the right smaller element of every element in the array. Note: If there is no smaller element on right side or left side of any element then we take zero as the smaller element. For example f 12 min read Delete consecutive same words in a sequenceGiven an array of n strings arr[]. The task is to determine the number of words remaining after pairwise destruction. If two consecutive words in the array are identical, they cancel each other out. This process continues until no more eliminations are possible. Examples: Input: arr[] = ["gfg", "for 7 min read Check mirror in n-ary treeGiven two n-ary trees, determine whether they are mirror images of each other. Each tree is described by e edges, where e denotes the number of edges in both trees. Two arrays A[]and B[] are provided, where each array contains 2*e space-separated values representing the edges of both trees. Each edg 11 min read Reverse a number using stackGiven a number , write a program to reverse this number using stack.Examples: Input : 365Output : 563Input : 6899Output : 9986We have already discussed the simple method to reverse a number in this post. In this post we will discuss about how to reverse a number using stack.The idea to do this is to 5 min read Reversing the first K elements of a QueueGiven an integer k and a queue of integers, The task is to reverse the order of the first k elements of the queue, leaving the other elements in the same relative order.Only following standard operations are allowed on the queue. enqueue(x): Add an item x to rear of queuedequeue(): Remove an item fr 13 min read Article Tags : Stack Queue Technical Scripter DSA deque +1 More Practice Tags : DequeQueueStack Like