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LeetCode 1836: Remove Duplicates From an Unsorted Linked List Solution

Master LeetCode problem 1836 (Remove Duplicates From an Unsorted Linked List), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

1836. Remove Duplicates From an Unsorted Linked List

Medium
Hash TableLinked List

Problem Explanation

Explanation:

To remove duplicates from an unsorted linked list, we can use a hash set to keep track of unique values encountered so far. We iterate through the linked list, adding each value to the hash set. If a value is already in the hash set, we remove it from the linked list. This way, we ensure that only unique values remain in the linked list.

Algorithm:

  1. Initialize a hash set to store unique values.
  2. Initialize two pointers, prev and current, to traverse the linked list.
  3. Traverse the linked list:
    • If the current value is not in the hash set, add it to the set and move both pointers to the next node.
    • If the current value is in the hash set, remove the current node by updating prev's next pointer.
  4. Return the modified linked list.

Time Complexity: O(N) where N is the number of nodes in the linked list. Space Complexity: O(N) for the hash set to store unique values.

:

Solution Code

public ListNode removeDuplicates(ListNode head) {
    Set<Integer> set = new HashSet<>();
    ListNode dummy = new ListNode(0);
    dummy.next = head;
    ListNode prev = dummy;
    ListNode current = head;
    
    while (current != null) {
        if (!set.contains(current.val)) {
            set.add(current.val);
            prev = current;
        } else {
            prev.next = current.next;
        }
        current = current.next;
    }
    
    return dummy.next;
}

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