LeetCode-82. Remove Duplicates from Sorted List IILevel up your coding skills and quickly land a job. This is the best place to expand your knowledge and get prepared for your next interview.https://leetcode.com/problems/remove-duplicates-from-sorted-list-ii/

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.

【C++】

/**
 * 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) {}
 * };
 */

1. 循环

class Solution {
public:
    ListNode* deleteDuplicates(ListNode* head) {
        ListNode *dummy = new ListNode(-1), *cur = dummy;
        dummy->next = head;
        while (cur->next && cur->next->next) {
            if (cur->next->val == cur->next->next->val) {
                int x = cur->next->val;
                while (cur->next && cur->next->val == x) {
                    //ListNode* freeNode = cur->next;
                    cur->next = cur->next->next;
                    //delete freeNode;
                    //freeNode == nullptr;
                }
            } else {
                cur = cur->next;
            }
        }
        return dummy->next;
    }
};

2. 递归

class Solution {
public:
    ListNode* deleteDuplicates(ListNode* head) {
        if (head == nullptr || head->next == nullptr) {return head;}
        if (head->val != head->next->val) {
            head->next = deleteDuplicates(head->next);
            return head;
        }
        ListNode* tmp = head->next;
        while (tmp != nullptr && tmp->val == head->val) {tmp = tmp->next;}
        return deleteDuplicates(tmp);
    }
};

【Java】

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */

1. 循环

class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        ListNode dummy = new ListNode(-1), cur = dummy;
        dummy.next = head;
        while (cur.next != null && cur.next.next != null) {
            if (cur.next.val == cur.next.next.val) {
                int x = cur.next.val;
                while (cur.next != null && cur.next.val == x) {
                    cur.next = cur.next.next;
                }
            } else {
                cur = cur.next;
            }
        }
        return dummy.next;
    }
}

2. 递归

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

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LeetCode-83. Remove Duplicates from Sorted List [C++][Java]_贫道绝缘子的博客-CSDN博客Given theheadof a sorted linked list,delete all duplicates such that each element appears only once. Returnthe linked listsortedas well.https://blog.csdn.net/qq_15711195/article/details/122394297