/* Amortized O(1), worst-case O(n) */
public AmortizedPQueue<E> minus() {
if (size() == 0) {
return this;
}
int fsize = front.size();
if (fsize == 0) {
// If there's nothing on front, dump back onto front
// (as stacks, this goes in reverse like we want)
// and take one off.
return new AmortizedPQueue<E>(Empty.<E>stack().plusAll(back), Empty.<E>stack()).minus();
} else if (fsize == 1) {
// If there's one element on front, dump back onto front,
// but now we've already removed the head.
return new AmortizedPQueue<E>(Empty.<E>stack().plusAll(back), Empty.<E>stack());
} else {
// If there's more than one on front, we pop one off.
return new AmortizedPQueue<E>(front.minus(0), back);
}
}
/* Worst-case O(1) */
public E peek() {
if (size() == 0) {
return null;
}
return front.get(0);
}
/* Worst-case O(1) */
@Override
public int size() {
return front.size() + back.size();
}