We have discussed Linked List Introduction and Linked List Insertion in previous posts on singly linked list.
Let us formulate the problem statement to understand the deletion process. Given a ‘key’, delete the first occurrence of this key in linked list.
To delete a node from linked list, we need to do following steps.
1) Find previous node of the node to be deleted.
2) Change the next of previous node.
3) Free memory for the node to be deleted.
Since every node of linked list is dynamically allocated using malloc() in C, we need to call free() for freeing memory allocated for the node to be deleted.
C/C++
// A complete working C program to demonstrate deletion in singly // linked list #include <stdio.h> #include <stdlib.h> // 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 the first occurrence of key in linked list */void deleteNode(struct Node **head_ref, int key) { // Store head node struct Node* temp = *head_ref, *prev; // If head node itself holds the key to be deleted if (temp != NULL && temp->data == key) { *head_ref = temp->next; // Changed head free(temp); // free old head return; } // 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 } // 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, 1); push(&head, 3); push(&head, 2); puts("Created Linked List: "); printList(head); deleteNode(&head, 1); puts("
Linked List after Deletion of 1: "); printList(head); return 0; } |
Java
// A complete working Java program to demonstrate deletion in singly // linked list class LinkedList { Node head; // head of list /* Linked list Node*/ class Node { int data; Node next; Node(int d) { data = d; next = null; } } /* Given a key, deletes the first occurrence of key in linked list */ void deleteNode(int key) { // Store head node Node temp = head, prev = null; // If head node itself holds the key to be deleted if (temp != null && temp.data == key) { head = temp.next; // Changed head return; } // Search for the key to be deleted, keep track of the // previous node as we need to change temp.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; } /* Inserts a new Node at front of the list. */ public void push(int new_data) { Node new_node = new Node(new_data); new_node.next = head; head = new_node; } /* This function prints contents of linked list starting from the given node */ public void printList() { Node tnode = head; while (tnode != null) { System.out.print(tnode.data+" "); tnode = tnode.next; } } /* Drier program to test above functions. Ideally this function should be in a separate user class. It is kept here to keep code compact */ public static void main(String[] args) { LinkedList llist = new LinkedList(); llist.push(7); llist.push(1); llist.push(3); llist.push(2); System.out.println("
Created Linked list is:"); llist.printList(); llist.deleteNode(1); // Delete node at position 4 System.out.println("
Linked List after Deletion at position 4:"); llist.printList(); } } |
Python
# Python program to delete a node from linked list # Node class class Node: # Constructor to initialize the node object def __init__(self, data): self.data = data self.next = None class LinkedList: # Function to initialize head def __init__(self): self.head = None # Function to insert a new node at the beginning def push(self, new_data): new_node = Node(new_data) new_node.next = self.head self.head = new_node # Given a reference to the head of a list and a key, # delete the first occurence of key in linked list def deleteNode(self, key): # Store head node temp = self.head # If head node itself holds the key to be deleted if (temp is not None): if (temp.data == key): self.head = temp.next temp = None return # Search for the key to be deleted, keep track of the # previous node as we need to change 'prev.next' while(temp is not None): if temp.data == key: break prev = temp temp = temp.next # if key was not present in linked list if(temp == None): return # Unlink the node from linked list prev.next = temp.next temp = None # Utility function to print the linked LinkedList def printList(self): temp = self.head while(temp): print " %d" %(temp.data), temp = temp.next # Driver program llist = LinkedList() llist.push(7) llist.push(1) llist.push(3) llist.push(2) print "Created Linked List: "llist.printList() llist.deleteNode(1) print "
Linked List after Deletion of 1:"llist.printList() # This code is contributed by Nikhil Kumar Singh (nickzuck_007) |
Output:
Created Linked List: 2 3 1 7 Linked List after Deletion of 1: 2 3 7
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