Algorithm Puzzles: Remove Linked List Elements

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Algorithm Puzzles everyday every week sometimes: Remove Linked List Elements

Puzzle

Puzzle from leetcode:

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.

Solution

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/**
 * 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* last = nullptr;
        ListNode* newHead = nullptr;
        ListNode* current = head;

        while(current) {
            if(current->val == val) {
                if(last) {
                    last->next = current->next;
                }
            } else {
                last = current;
                if(!newHead) {
                    newHead = last;
                }
            }
            current = current->next;
        }

        return newHead;
    }
};

T.C. O(N)