Is Remove Duplicates From an Unsorted Linked List easy or hard?

The problem is generally classified as Medium difficulty. It requires combining hash table frequency counting with careful linked list pointer manipulation, which is slightly more involved than basic traversal problems.

Remove Duplicates From an Unsorted Linked List Python/Java solution

Implement a two-pass algorithm. In the first pass, store value counts in a dictionary (Python) or HashMap (Java). In the second pass, traverse the list with a dummy node and remove any node whose frequency is greater than one.

How to solve Remove Duplicates From an Unsorted Linked List in O(n)?

Use a hash map to record how many times each value appears in the list. After building the frequency map in one traversal, iterate through the list again and delete any node whose value appears more than once. Each node is processed a constant number of times, resulting in O(n) time complexity.

What is the best approach for Remove Duplicates From an Unsorted Linked List?

The most efficient approach uses a hash table to count how many times each value appears in the linked list. First traverse the list to build a frequency map, then perform a second pass to remove nodes whose frequency is greater than one. This method runs in O(n) time with O(n) extra space.

Is Remove Duplicates From an Unsorted Linked List asked at Google/Amazon/Meta?

Linked list deduplication and frequency-based removal problems commonly appear in interviews at companies like Amazon, Google, and Meta. Variations test knowledge of hash tables, pointer manipulation, and efficient list traversal.

What data structure is used in Remove Duplicates From an Unsorted Linked List?

The optimal solution relies on a hash table (or hash map) to store value frequencies. The linked list itself is traversed while pointers are adjusted to remove nodes with duplicate values.

What is the time complexity of Remove Duplicates From an Unsorted Linked List?

The optimal solution runs in O(n) time because the linked list is traversed twice: once to count frequencies and once to remove duplicate nodes. Hash table operations are O(1) on average. A naive brute force solution would take O(n²) time due to repeated scanning of the list.

Description Hints 2 Solution Video 4:49

1836. Remove Duplicates From an Unsorted Linked List

Medium75.6% acceptance2 companiesPremium elsewhere, free here

Given the head of a linked list, find all the values that appear more than once in the list and delete the nodes that have any of those values.

Return the linked list after the deletions.

Example 1:


Input: head = [1,2,3,2]

Output: [1,3]

Explanation: 2 appears twice in the linked list, so all 2's should be deleted. After deleting all 2's, we are left with [1,3].

Example 2:


Input: head = [2,1,1,2]

Output: []

Explanation: 2 and 1 both appear twice. All the elements should be deleted.

Example 3:


Input: head = [3,2,2,1,3,2,4]

Output: [1,4]

Explanation: 3 appears twice and 2 appears three times. After deleting all 3's and 2's, we are left with [1,4].

Constraints:

The number of nodes in the list is in the range [1, 10⁵]
1 <= Node.val <= 10⁵

Asked at 2 companies

Microsoft Amazon

Topics

Hash Table Linked List

Hints open one at a time

Hint 1

Is there a way we can know beforehand which nodes to delete?

Hint 2

Count the number of appearances for each number.

4:49

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