delete first node in linked list c++ - Wikitechy

Delete all occurrences of a given key in a linked list ?

Editor — Tue, 13 Jul 2021 17:39:53 +0000

Delete all occurrences of a given key in a linked list ?

Given a singly linked list, delete all occurrences of a given key in it. For example,
 
Input:  2 -> 1 -> 8 -> 2 ->  3 ->  2 -> 7
       Key to delete = 2
Output:  1 -> 8 -> 3 -> 7 
Sample Code in C 
#include  
#include  
// A linked list node 
struct Node 
{ 
    int data; 
    struct Node *next; 
}; 
/* Given a reference (pointer to pointer) to the head of a list 
   and an int, inserts a new node on the front of the list. */
void push(struct Node** head_ref, int new_data) 
{ 
    struct Node* new_node = (struct Node*) malloc(sizeof(struct Node)); 
    new_node->data  = new_data; 
    new_node->next = (*head_ref); 
    (*head_ref)    = new_node; 
} 
/* Given a reference (pointer to pointer) to the head of a list and 
   a key, deletes all occurrence of the given key in linked list */
void deleteKey(struct Node **head_ref, int key) 
{ 
    // Store head node 
    struct Node* temp = *head_ref, *prev; 
    // If head node itself holds the key or multiple occurrences of key 
    while (temp != NULL && temp->data == key) 
    { 
        *head_ref = temp->next;   // Changed head 
        free(temp);               // free old head 
        temp = *head_ref;         // Change Temp 
    } 
    // Delete occurrences other than head 
    while (temp != NULL) 
    { 
        // Search for the key to be deleted, keep track of the 
        // previous node as we need to change 'prev->next' 
        while (temp != NULL && temp->data != key) 
        { 
            prev = temp; 
            temp = temp->next; 
        } 
        // If key was not present in linked list 
        if (temp == NULL) return; 
        // Unlink the node from linked list 
        prev->next = temp->next; 
        free(temp);  // Free memory 
        //Update Temp for next iteration of outer loop 
        temp = prev->next; 
    } 
} 
// This function prints contents of linked list starting from 
// the given node 
void printList(struct Node *node) 
{ 
    while (node != NULL) 
    { 
        printf(" %d ", node->data); 
        node = node->next; 
    } 
} 
   /* Drier program to test above functions*/
int main() 
{ 
    /* Start with the empty list */
    struct Node* head = NULL; 
    push(&head, 7); 
    push(&head, 2); 
    push(&head, 3); 
    push(&head, 2); 
    push(&head, 8); 
    push(&head, 1); 
    push(&head, 2); 
    push(&head, 2); 
    int key = 2; // key to delete 
    puts("Created Linked List: "); 
    printList(head); 
    deleteKey(&head, key); 
    puts("\nLinked List after Deletion: "); 
    printList(head); 
    return 0; 
}

Output


Created Linked List:
 2  2  1  8  2  3  2  7
Linked List after Deletion:
 1  8  3  7 

How to delete an element in a linked list ?

Editor — Tue, 13 Jul 2021 16:57:20 +0000

How to delete an element in a linked list ?

To delete a node from linked list, we need to do following steps:
- Find previous node of the node to be deleted.
- Change the next of previous node.
- Free memory for the node to be deleted

Example

Input: position = 1, Linked List = 9->2->3->7->6
Output: Linked List =  9->3->7->6

Input: position = 0, Linked List = 9->2->3->7->6
Output: Linked List = 2->3->7->6

Sample code

#include  
#include  

// A linked list node 
struct Node 
{ 
	int data; 
	struct Node *next; 
}; 

/* Given a reference (pointer to pointer) to the head of a list 
and an int, inserts a new node on the front of the list. */
void push(struct Node** head_ref, int new_data) 
{ 
	struct Node* new_node = (struct Node*) malloc(sizeof(struct Node)); 
	new_node->data = new_data; 
	new_node->next = (*head_ref); 
	(*head_ref) = new_node; 
} 

/* Given a reference (pointer to pointer) to the head of a list 
and a position, deletes the node at the given position */
void deleteNode(struct Node **head_ref, int position) 
{ 
// If linked list is empty 
if (*head_ref == NULL) 
	return; 

// Store head node 
struct Node* temp = *head_ref; 

	// If head needs to be removed 
	if (position == 0) 
	{ 
		*head_ref = temp->next; // Change head 
		free(temp);			 // free old head 
		return; 
	} 

	// Find previous node of the node to be deleted 
	for (int i=0; temp!=NULL && i		temp = temp->next; 

	// If position is more than number of ndoes 
	if (temp == NULL || temp->next == NULL) 
		return; 

	// Node temp->next is the node to be deleted 
	// Store pointer to the next of node to be deleted 
	struct Node *next = temp->next->next; 

	// Unlink the node from linked list 
	free(temp->next); // Free memory 

	temp->next = next; // Unlink the deleted node from list 
} 

// This function prints contents of linked list starting from 
// the given node 
void printList(struct Node *node) 
{ 
	while (node != NULL) 
	{ 
		printf(" %d ", node->data); 
		node = node->next; 
	} 
} 

/* Drier program to test above functions*/
int main() 
{ 
	/* Start with the empty list */
	struct Node* head = NULL; 

	push(&head, 6); 
	push(&head, 7); 
	push(&head, 3); 
	push(&head, 2); 
	push(&head, 9); 

	puts("Created Linked List: "); 
	printList(head); 
	deleteNode(&head, 4); 
	puts("\nLinked List after Deletion at position 4: "); 
	printList(head); 
	return 0; 
}

Output:

Created Linked List: 
 9  2  3  7  6 
Linked List after Deletion at position 4: 
 9  2  3  7