public void delete(int val) {
ListNode p = head, prev = null;
while (p != null && p.value != val) {
prev = p;
p = p.nextNode;
}
if (p != null) {
if (p == head) head = p.nextNode;
else prev.nextNode = p.nextNode;
if (tail == p) tail = prev;
}
}
public void append(int value) {
ListNode p = new ListNode(value);
if (head == null) head = p;
else tail.nextNode = p;
tail = p;
}
public void prepend(int val) {
ListNode p = new ListNode(val);
p.nextNode = head;
head = p;
}