Delete a Node from linked list without head pointer

You are given a singly linked list and pointer which is pointing to the node which is required to be deleted. Any information about head pointer or any other node is not given. You need to write a function to delete that node from linked list. Your function will take only one argument: pointer to the node which is to be deleted.

Examples:
A linked list is built as:

Defination of each node is as follows: 
struct Node {
    int data;
    struct Node* next;
};

Input : C (a pointer to C)
Output : A-->B-->D-->E-->F

Input : A (a pointer to A)
Output : B-->D-->E-->F

It would be a simple deletion problem from singly linked list if the head pointer was given because for deletion you must know the previous node and you can easily reach there by traversing from head pointer. Conventional deletion is impossible without knowledge of previous node of node which need to be deleted.

The trick here is we can copy the data of next node to the data field of current node to be deleted. Then we can move one step forward. Now our next has become the current node and current has become previous node. Now we can easily delete the current node by conventional deletion methods.

For example, suppose we need to delete C and a pointer to C is given. If we had a pointer to B we could have deleted C easily. But here we will copy the data field of D to data field of C. Then we will move forward. Now we are at D and we have a pointer to C i.e. the previous pointer. So we will delete D. That’s how the node C will be deleted.

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void deleteNodeWithoutHead(struct Node* pos)
{
    if (*pos == NULL) // If linked list is empty
        return;
  
    else {
        struct Node* temp = pos->next;
  
        // Copy data of the next node to current node
        pos->data = pos->next->data; 
  
        // Perform conventional deletion
        pos->next = pos->next->next; 
  
        free(temp);
    }
    return 0;
}

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This article is contributed by Jeet Jain. Please see Given only a pointer to a node to be deleted in a singly linked list, how do you delete it? for more details and complete implementation.



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Hi I am Jeet Jain I am a final year undergrad student a full stack web developer competitive and self motivated person This blog is a medium to share my experience and learnings from life

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