Delete keys in a Linked list using C++ program

Delete keys in a Linked list: In this tutorial, we will learn how to delete keys in a given linked list using the C++ program? By Souvik Saha Last updated : August 01, 2023

Problem statement

Given a linked list and a key element, we have to delete the node from the linked list.

Example

If a linked list is like : 1 → 2 → 3 → 4 → 5 → 6

Case 1: When key is not head
The key value is 4
After deleting that node the linked list is:1 → 2 → 3 → 5 → 6
    
Case 2: When key is head
The key value is 1
After deleting that node the linked list is: 2 → 3 → 5 → 6

Algorithm

To solve the problem there are two conditions,

If the key node is the head of the linked list then we delete the node and point the head pointer to next node.
If the key is not the head pointer of the linked list then simply delete that node.

C++ program to delete keys in a linked list

#include <bits/stdc++.h>
using namespace std;

struct node {
    int data;
    node* next;
};

//Create a new node
struct node* create_node(int x)
{
    struct node* temp = new node;
    temp->data = x;
    temp->next = NULL;
    return temp;
}

//Enter the node into the linked list
void push(node** head, int x)
{
    struct node* store = create_node(x);
    if (*head == NULL) {
        *head = store;
        return;
    }
    struct node* temp = *head;
    while (temp->next) {
        temp = temp->next;
    }
    temp->next = store;
}

//Delete the middle node from the linked list
void delete_node(node** head, int x)
{
    if ((*head)->next == NULL) {
        *head = NULL;
        return;
    }
    struct node* temp = *head;
    if (temp->data == x) {
        temp = temp->next;
        *head = temp;
        return;
    }
    while (temp) {
        if (temp->data == x) {
            temp->data = temp->next->data;
            temp->next = temp->next->next;
            break;
        }
        temp = temp->next;
    }
}

//Print the list
void print(node* head)
{
    struct node* temp = head;
    while (temp) {
        cout << temp->data << " ";
        temp = temp->next;
    }
}

int main()
{
    struct node* l = NULL;
    
    push(&l, 1);
    push(&l, 2);
    push(&l, 3);
    push(&l, 4);
    push(&l, 5);
    push(&l, 6);
    
    cout << "Before the delete operation" << endl;
    print(l);
    
    delete_node(&l, 2);
    
    cout << "\nAfter the delete operation" << endl;
    print(l);

    return 0;
}

Output

Before the delete operation
1 2 3 4 5 6
After the delete operation
1 3 4 5 6