Remove duplicates from a singly linked list
Company: Salesforce
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: medium
Interview Round: HR Screen
You are given the head of a **singly linked list** of integers. Modify the list **in place** so that it contains **only the first occurrence** of each value (i.e., remove any node whose value has already appeared earlier in the list).
- Each node has fields:
- `data` (integer)
- `next` (reference to next node, or `null` at the tail)
- The **relative order** of the remaining nodes must stay the same.
Return the head of the updated linked list.
### Examples
1. Input: `3 -> 4 -> 3 -> 6`
Output: `3 -> 4 -> 6`
2. Input: `3 -> 4 -> 3 -> 2 -> 6 -> 1 -> 2 -> 6`
Output: `3 -> 4 -> 2 -> 6 -> 1`
Quick Answer: This question evaluates understanding of singly linked list data structures and in-place node manipulation to remove repeated values while preserving relative order, testing competencies in pointer management and duplicate-detection.