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0083. Remove Duplicates from Sorted List

Problem
Leetcode 83. Remove Duplicates from Sorted List
Difficulty 🟢 Easy
Tags Linked List

Given the head of a sorted linked list, delete all duplicates such that each element appears only once. Return the linked list sorted as well.

Examples

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

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

Constraints

  • 0 <= number of nodes <= 300
  • -100 <= Node.val <= 100
  • The list is guaranteed to be sorted.

Approach

Walk the list with a single pointer cur. If cur.next.val == cur.val, skip the next node by cur.next = cur.next.next. Otherwise advance.

Complexity

  • Time: O(n)
  • Space: O(1)

Implementation

Go

type ListNode struct { Val int; Next *ListNode }

func deleteDuplicates(head *ListNode) *ListNode {
    cur := head
    for cur != nil && cur.Next != nil {
        if cur.Next.Val == cur.Val {
            cur.Next = cur.Next.Next
        } else {
            cur = cur.Next
        }
    }
    return head
}

Java

class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        ListNode cur = head;
        while (cur != null && cur.next != null) {
            if (cur.next.val == cur.val) cur.next = cur.next.next;
            else cur = cur.next;
        }
        return head;
    }
}

Python

class Solution:
    def deleteDuplicates(self, head):
        cur = head
        while cur and cur.next:
            if cur.next.val == cur.val:
                cur.next = cur.next.next
            else:
                cur = cur.next
        return head

Edge Cases

  • Empty list / single node: unchanged.
  • All duplicates: collapses to one node.
  • No duplicates: unchanged.

Visual Animation

animation.html