82. Remove Duplicates from Sorted List II

82. Remove Duplicates from Sorted List II

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

For example,
Given 1->2->3->3->4->4->5, return 1->2->5.
Given 1->1->1->2->3, return 2->3.

注意：head -> next -> val，也必须判断head -> next != nullptr;

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* deleteDuplicates(ListNode* head) {
        if(head == nullptr){
            return nullptr;            
        }
        ListNode* dummyNode = new ListNode(-1);
        dummyNode -> next  = head;
        head = dummyNode;
        
        while(head -> next != nullptr && head -> next -> next != nullptr){
            
            if(head -> next -> val == head -> next -> next -> val){
                int flag = head -> next -> val;
                while(flag == head -> next -> val){
                    head -> next = head -> next -> next;
                    if(head == nullptr || head -> next == nullptr){
                        break;
                    }
                }
            }
            else{
                head = head -> next;
            }
            
        }
        return dummyNode -> next;
    }
};