循环双链表indexOf和remove函数不正确

Question

I am currently implementing a circular doubly-linked list with a dummy head node. My add functions (adding an element at a given index, at the start, or at the end) seem to work flawlessly, but I cannot extrapolate to make a functioning indexOf (which returns the index of an element) or remove (remove node at given index) method.

When debugging, indexOf seems to grab the wrong index. When given a list of:

[Alabama, Alaska, Arizona, Arkansas, Wyoming, California]

Calling

list.remove(indexOf("Wyoming"));

Returns

[Alabama, Alaska, Arizona, Arkansas, Wyoming, ]

Here is the indexOf function:

public int indexOf(E e) {
    Node<E> current = head;
    for (int i = 0; i < size; i++) {
        if (e.equals(current.element)) {
            return i;
        }
        current = current.next;
    }
    return -1;
}

And here is the remove function:

public E remove(int index) {
    if (index < 0 || index >= size) {
        throw new NoSuchElementException();
    } else if (index == 0) {
        return removeFirst();
    } else if (index == size - 1) {
        return removeLast();
    } else {


        Node<E> previous = head;
        for (int i = 1; i < index; i++) {
            previous = previous.next;
        }
        Node<E> current = previous.next;
        previous.next = current.next;
        size--;
        return current.element;

    }
}

Answer 1

If head should always be null , then your indexOf() method doesn't seem correct

public int indexOf(E e) {
    Node<E> current = head.next; // Add this to effectively begin with the first index of your list
    for (int i = 0; i < size; i++) {
        if (e.equals(current.element)) { // This will never be equals, because of the first time current being null
            return i;
        }
        current = current.next;
    }
    return -1;
}