203. Remove Linked List Elements

/**
 * 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) {
        //it means if head-> val == val skip these nodes 
        while(head != NULL && head -> val == val)
        {
            head = head -> next;
        }

        //if all the values of nodes are equal to val means head == NULL . so, list is empty 
        if(head == NULL)
            return NULL;
        
        ListNode* temp = head;

        //it means atleast one node is present so (temp -> next) is exists.
        while(temp -> next != NULL)
        {

            // if the next node is equal then skip the node
            if(temp ->next -> val == val)
            {
                ListNode* nodeToDelete = temp -> next;
                ListNode* next_node = temp -> next -> next;

                delete(nodeToDelete);
                temp -> next = next_node;
            }
            //otherwise go ahead
            else 
            {
                temp = temp -> next;
            }
        }

        return head;
    }
};