203. Remove Linked List Elements

 203. Remove Linked List Elements

Given the head of a linked list and an integer val, remove all the nodes of the linked list that has Node.val == val, and return the new head.

 

Example 1:

Input: head = [1,2,6,3,4,5,6], val = 6
Output: [1,2,3,4,5]

Example 2:

Input: head = [], val = 1
Output: []

Example 3:

Input: head = [7,7,7,7], val = 7
Output: []

 

Constraints:

• The number of nodes in the list is in the range [0, 104].
• 1 <= Node.val <= 50
• 0 <= val <= 50

Solution in 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) {}

 * };

 */

class Solution {

public:

    ListNode* removeElements(ListNode* head, int val) {

        ListNode* temp=head;

        ListNode* ans;

        if(head==NULL){

            return NULL;

        }

        while(temp->val==val){

            if(temp->next==NULL){

                return NULL;

            }

            temp=temp->next;

        }

        ans=temp;

        while(temp->next!=NULL){

            if(temp->next->val==val){

              ListNode* left=temp;

                while(temp->next->val==val){

                    

                   temp=temp->next; 

                    if(temp->next==NULL){

                        left->next=NULL;

                        return ans;

                    }

                }

                left->next=temp->next;

            }

            else{

                temp=temp->next;

            }

            

            

        }

        return ans;

        

    }

};