Singly Linked List – Delete Node

Question: You are given a pointer to a node (not the tail node) in a singly linked list. Delete that node from the linked list. Write code in C.
Answer: To delete a node, you have to redirect the next pointer of the previous node to point to the next node instead of the current one. Since we don’t have a pointer to the previous node, we can’t redirect its next pointer. So what do we do?
We can easily get away by moving the data from the next node into the current node and then deleting the next node.  This solution has O(1) runtime. Here’s some code to illustrate this simple logic.
void deleteNode( Node * node )
{
    Node * temp = node->next;
    node->data = node->next->data;
    node->next = temp->next;
    free(temp);
}

Some things to consider. This method could pose potential problems. For instance, let’s consider we have a linked list A -> B -> C -> D and we are given a pointer to B to delete it. Theoretically, you would expect B to be deleted and all pointers which were pointing to B to become invalid. However, if we use this function to delete B, all pointers which were pointing to B will still be valid. Furthermore, node B now will contain the value C and node C will be invalid. Any previous pointers to C will become invalid, which may not be expected behavior in general. This is not a problem if there are no external links to any of the items in the linked list. But this would definitely be something you should consider asking your interviewer to show your thinking process.

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