82. 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.

/**
 * 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) {
        if(!head or !head->next) return head;
        while(head and head->next and head->val == head->next->val) {
            int v = head->val;
            while(head && head->val == v) head = head->next;
        }

        if(head) {
            head->next = deleteDuplicates(head->next);
        }

        return head;
    }
};

/**
 * 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* tmp = new ListNode(0, head);
        ListNode* prev = tmp;
        while(head) {
            while(head and head->next and head->val == head->next->val) {
                int v = head->val;
                while(head && head->val == v) head = head->next;
            }
            prev->next = head;
            prev = head;
            if(head) head = head->next;
        }
        return tmp->next;
    }
};