121RemoveLinkedListElements.cpp

#include <iostream>
using namespace std;

struct ListNode {
    int val;
    ListNode* next;

    ListNode(int x) : val(x), next(nullptr) {}
};

class Solution {
public:
    ListNode* removeElements(ListNode* head, int val) {
        ListNode dummy(0);
        dummy.next = head;

        ListNode* prev = &dummy;
        ListNode* curr = head;

        while (curr) {
            if (curr->val == val) {
                prev->next = curr->next;  // remove node
            } else {
                prev = curr;              // move prev only if not deleted
            }
            curr = curr->next;
        }

        return dummy.next;
    }
};

// Helper function to print list
void printList(ListNode* head) {
    while (head) {
        cout << head->val;
        if (head->next) cout << " -> ";
        head = head->next;
    }
    cout << endl;
}

int main() {

    // Build linked list: 1->2->6->3->4->5->6
    ListNode* head = new ListNode(1);
    head->next = new ListNode(2);
    head->next->next = new ListNode(6);
    head->next->next->next = new ListNode(3);
    head->next->next->next->next = new ListNode(4);
    head->next->next->next->next->next = new ListNode(5);
    head->next->next->next->next->next->next = new ListNode(6);

    cout << "Original List: ";
    printList(head);

    Solution obj;
    head = obj.removeElements(head, 6);

    cout << "After Removing 6: ";
    printList(head);

    return 0;
}