public class FinalReview {

    // For LinkedIntList programming, the method would be added to the LinkedIntList class

    // A good exercise to understand how this works is to draw out a picture and verifies
    // if it works by hand!
    public LinkedIntList removeFirstOf3() {
        // Common Bug: Mixing up LinkedIntList and ListNode
        LinkedIntList other = new LinkedIntList();
        if (front != null) { // Common Bug: Forgetting empty case
            // Set up front of other list, keep reference to end of list so we can add there
            other.front = front;
            ListNode back1 = other.front;

            // Update our front to remove first value, current will be pointing to
            // second node in original group
            front = front.next;
            ListNode current = front;

            // Common Bug: Having a slightly wrong loop condition that doesn't check all
            // the nulls it needs
            while (current != null && current.next != null &&
                    current.next.next != null) {
                current = current.next;

                // Move this node to the end of the other list
                back1.next = current.next;
                back1 = back1.next;

                // Update current to be in correct next position
                current.next = current.next.next;
                current = current.next;
            }
            // Common Bug: Forgetting to set fields to null if necessary
            back1.next = null;
        }

        // Common Bug: Forgetting to return
        return other;
    }

    // For Binary Tree programming, the method would be added to the IntTree class

    // A good exercise to understand how this works is to draw out a picture and verifies
    // if it works by hand!
    public void completeToLevel(int target) {
        if (target < 1) {
            throw new IllegalArgumentException();
        }
        overallRoot = complete(overallRoot, target, 1);
    }

    private IntTreeNode complete(IntTreeNode root, int target, int level) {
        if (level <= target) {
            // Commnon Bug: Mixing up logic and not realizing we don't want an else branch for recursion
            if (root == null) {
                root = new IntTreeNode(-1);
            }

            // Common Bug: Forgetting x=change(x) pattern if it's necessary
            root.left = complete(root.left, target, level + 1);
            root.right = complete(root.right, target, level + 1);
        }
        return root;
    }
}