035_Linked List Cycle II.cpp

Node *firstNode(Node *head)
{
    //    Write your code here.

    Node* fast = head;
    Node* slow = head;

    while(fast and fast->next)
    {
        fast = fast->next->next;
        slow = slow->next;

        if(fast == slow)
        {
            while(head != slow)
            {
                head = head->next;
                slow = slow->next;
            }
            return head;
        }
    }

    
    return nullptr;

}