82. Remove Duplicates from Sorted List II

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82. Remove Duplicates from Sorted List II

Description

Difficulty: Medium

Related Topics: Linked List, Two Pointers

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:

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

Example 2:

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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.

Hints/Notes

  • two pointers

Solution

Language: C++

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/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* deleteDuplicates(ListNode* head) {
        ListNode dummy(0);
        ListNode *p = &dummy, *q = head;
        while (q) {
            if (q->next && q->val == q->next->val) {
                while (q->next && q->val == q->next->val) {
                    q = q->next;
                }
                if (!q->next) {
                    p->next = nullptr;
                }
                q = q->next;
            } else {
                p->next = q;
                p = p->next;
                q = q->next;
            }
        }
        return dummy.next;
    }
};