82. Remove Duplicates from Sorted List II

82. Remove Duplicates from Sorted List II | LeetCode Solution

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.

/**
 * 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==NULL or head->next==NULL)return head;
     ListNode* temp=head;
     ListNode* prev=head;
     unordered_map<int,int>m;
        while(temp!=NULL){
            m[temp->val]++;
            temp=temp->next;
        }
        ListNode* ans=NULL;
        bool found=false;
        temp=head;
     while(temp!=NULL){
         auto it=m.find(temp->val);
         if(it->second==1){
            prev=temp;
             if(!found){
                 ans=temp;
                 found=true;
             }
         }
         else{
             if(temp->next!=NULL){
             prev->next=temp->next;
            //  cout<<temp->data<<endl;
         }
         else{
             prev->next=NULL;
         }
         }
        temp=temp->next;

     }
     return ans;
    }
};