Linked List

Floyd's fast and slow pointer

C++

ListNode* slow = head;
ListNode* fast = head;
while (fast != nullptr && fast->next != nullptr) {
    // do something here
    slow = slow->next;
    fast = fast->next->next;
}

Java

ListNode slow = head, fast = head;
while (fast != null && fast.next != null) {
    // do something here
    slow = slow.next;
    fast = fast.next.next;
}