Remove Duplicates From an Unsorted Linked List

MediumLinked Listhashing

Solve this the way you would in the interview: out loud, on a timer, with an AI interviewer asking follow-ups while you code. You get a scored report at the end.

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Problem

Given the head of a linked list whose values are in no particular order, find every value that occurs **more than once** and remove all nodes carrying those values. Every copy is removed, not just the extras. Keep the remaining nodes in their original relative order and return the new head. If every node is removed, return an empty list.

Examples

Input: head = [1,2,3,2]
Output: [1,3]
2 appears twice, so both nodes with value 2 are removed.
Input: head = [2,1,1,2]
Output: []
Both values repeat, so nothing is left.
Input: head = [3,2,2,1,3,2,4]
Output: [1,4]
3 and 2 repeat; only 1 and 4 occur once.

Constraints

  • 1 <= number of nodes <= 10^5
  • 1 <= Node.val <= 10^5

What the interviewer grades

A correct solution is one of five scores. The report also grades problem understanding (did you clarify inputs and edge cases before coding), problem solving, communication while you work, code quality, and testing. See a sample report, or read up on the pattern in the lessons.

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