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05double_ended_queue.cpp

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#include<bits/stdc++.h>

/*

pop and push at both ends at TC 0(1)

Implement using doubly LL

*/

using namespace std;

class Node{

public:

int val;

Node* prev;

Node* next;

Node (int val){

this->val = val;

this->prev = nullptr;

this->next = nullptr;

}

};

class Deque{

public:

Node *head;

Node *tail;

int size;

Deque(){

head = tail = NULL;

size = 0;

}

void push_back(int val){

Node *temp = new Node(val);

if(size == 0) tail = head = temp;

else{

tail->next = temp;

temp->prev = tail;

tail = temp;

}

size++;

}

void push_front(int val){

Node *temp = new Node(val);

if(size==0) head = tail = temp;

else{

temp->next = head;

head->prev = temp;

head = temp;

}

size++;

}

void pop_front(){

if(size==0){

cout<<"List is empty"<<endl;

return;

}

head = head->next;

head->prev = nullptr;

size--;

}

void pop_back(){

Node *temp = head;

while(temp->next != tail){

temp = temp->next;

}

temp->next = NULL;

tail->prev = nullptr;

tail = temp;

size--;

}

void display(){

Node *temp = head;

if(temp == NULL) cout<<"Linkedlist is empty!";

while(temp != NULL){

cout<<temp->val<<" ";

temp = temp->next;

}

cout<<endl;

}

int length(){

return size;

}

};

int main(){

Deque dq;

dq.push_back(10);

dq.push_back(20);

dq.push_back(30);

dq.push_back(40);

dq.push_back(50);

dq.push_back(60);

dq.display();

dq.push_front(5);

dq.display();

}