C++ - Delete the first node of the Doubly Linked List
In this method, the first node of the doubly linked list is deleted. For example - if the given list is 10->20->30->40 and the first node is deleted, the list becomes 20->30->40.
Deleting the first node of the Doubly Linked List is very easy. If the head is not null then create a temp node pointing to head and move head to the next of head. Then delete the temp node. If the new head is not null, make the prev of it as null.
The function pop_front is created for this purpose. It is a 4-step process.
void pop_front() { if(head != NULL) { //1. if head is not null, create a // temp node pointing to head Node* temp = head; //2. move head to next of head head = head->next; head //3. delete temp node free(temp); //4. If the new head is not null, then // make prev of the new head as null if(head != NULL) head->prev = NULL; } }
The below is a complete program that uses above discussed concept of deleting the first node of the doubly linked list.
#include <iostream> using namespace std; //node structure struct Node { int data; Node* next; Node* prev; }; class LinkedList { private: Node* head; public: LinkedList(){ head = NULL; } //Add new element at the end of the list void push_back(int newElement) { Node* newNode = new Node(); newNode->data = newElement; newNode->next = NULL; newNode->prev = NULL; if(head == NULL) { head = newNode; } else { Node* temp = head; while(temp->next != NULL) temp = temp->next; temp->next = newNode; newNode->prev = temp; } } //Delete first node of the list void pop_front() { if(head != NULL) { Node* temp = head; head = head->next; free(temp); if(head != NULL) head->prev = NULL; } } //display the content of the list void PrintList() { Node* temp = head; if(temp != NULL) { cout<<"The list contains: "; while(temp != NULL) { cout<<temp->data<<" "; temp = temp->next; } cout<<endl; } else { cout<<"The list is empty.\n"; } } }; // test the code int main() { LinkedList MyList; //Add four elements in the list. MyList.push_back(10); MyList.push_back(20); MyList.push_back(30); MyList.push_back(40); MyList.PrintList(); //Delete the first node MyList.pop_front(); MyList.PrintList(); return 0; }
The above code will give the following output:
The list contains: 10 20 30 40 The list contains: 20 30 40