82

82. Remove Duplicates from Sorted List II (Medium)

Given the head of a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list. Return the linked list sorted as well.

 

Example 1:

Input: head = [1,2,3,3,4,4,5]
Output: [1,2,5]

Example 2:

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

 

Constraints:

• The number of nodes in the list is in the range [0, 300].
• -100 <= Node.val <= 100
• The list is guaranteed to be sorted in ascending order.

Companies:
Amazon, Microsoft, ByteDance, Facebook

Related Topics:
Linked List, Two Pointers

Similar Questions:

• Remove Duplicates from Sorted List (Easy)
• Remove Duplicates From an Unsorted Linked List (Medium)

Solution 1.

// OJ: https://leetcode.com/problems/remove-duplicates-from-sorted-list-ii/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(1)
class Solution {
public:
    ListNode* deleteDuplicates(ListNode* head) {
        ListNode dummy, *tail = &dummy;
        while (head) {
            int val = head->val;
            if (head->next && head->next->val == val) {
                while (head && head->val == val) head = head->next;
            } else {
                tail->next = head;
                tail = head;
                head = head->next;
            }
        }
        tail->next = nullptr;
        return dummy.next;
    }
};