DSA interview question

Search for a Value in a Linked List

Medium · Data structures · Topics: linkedlist

The problem

A contacts app stores recently called numbers in a singly linked list, most recent first. When a call comes in, the app checks whether the number is already in the list and where, so it can move that entry to the front. There's no index and no ordering to exploit, so the only option is a linear scan from the head, counting positions until the value turns up or the list ends. It's the linked-list counterpart of linear search.

Example: 1 -> 2 -> 3 -> 4, search 3 → position 3.

Function signature

int searchPosition(Node* head, int key);  // 1-indexed position of the first match, or -1

Test cases

Input `(list, key)`	Output	Explanation
`(1 -> 2 -> 3 -> 4, 3)`	3
`(1 -> 2 -> 3 -> 4, 5)`	-1	Not present
`(empty, 1)`	-1
`(7 -> 7, 7)`	1	The first occurrence
`(4 -> -2 -> 9, 9)`	3	At the tail

(Confirm: positions are 1-indexed; return the first occurrence, or -1 if the key is absent.)

How interviewers phrase it

"Search for an element in a linked list" (GeeksforGeeks), usually returning true/false or the position.
"Write both iterative and recursive versions."

Clarifying questions to ask

Return a boolean, a position, or the node?
0-indexed or 1-indexed positions?
First occurrence or all occurrences?

Follow-ups to expect

"Can you use binary search on a sorted linked list?"
"What's the recursive version?"
"How would you move a found node to the front?"
"Complexity?"

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