DSA interview question

Delete the Head of a Linked List (and a Node at a Position)

Easy · Data structures · Topics: linkedlist

The problem

When the music player finishes a song, it must remove the head of the queue: the second song becomes the new head, and the old head's memory is freed. The same code base also removes a song at position k when the user swipes it away. Deleting the head is O(1): remember the old head, move head to head->next, free the old node. Deleting at position k needs the predecessor, so its next can skip over the removed node. As with insertion, the empty list and head deletion are the edge cases to get right.

Example: 1 -> 2 -> 3, delete the head → 2 -> 3.

Function signature

Node* deleteHead(Node* head);                   // returns the new head (nullptr if the list becomes empty)
Node* deleteAtPosition(Node* head, int pos);    // pos is 1-indexed and valid

Test cases

Input	Output list	Explanation
`deleteHead(1 -> 2 -> 3)`	`2 -> 3`
`deleteHead(5)`	`(empty)`	The only node is removed
`deleteHead(empty)`	`(empty)`	Nothing to delete
`deleteAtPosition(1 -> 2 -> 3 -> 4, 3)`	`1 -> 2 -> 4`	The middle node is removed
`deleteAtPosition(1 -> 2, 1)`	`2`	Position 1 is the head
`deleteAtPosition(1 -> 2 -> 3, 3)`	`1 -> 2`	The tail

(Confirm: positions are 1-indexed and valid; removed nodes are freed; the function returns the new head.)

How interviewers phrase it

"Delete the first node of a linked list" (GeeksforGeeks).
"Delete the node at position k," "delete the last node," "delete all nodes with value x."
"Delete a node when you're given only a pointer to that node" (LeetCode 237), a classic trick question.

Clarifying questions to ask

What should happen for an empty list?
Are positions 0- or 1-indexed?
Should deleted nodes be freed?

Follow-ups to expect

"Why do you need the predecessor to delete a middle node?"
"How do you delete a node given only a pointer to it (not the tail)?"
"How do you delete the tail?"
"How does a dummy head help?"
"Complexity?"

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