Java: How to tell if Two ArrayDeque are equal?

Question

Is there a way to tell if Two Array Deques are equal in Java? Stack has an .equals() operator?

What is data values equals method for Array Deque? this is what I wrote temporarily, however it removes items from the Deque. If there is no library method, any way to optimize code below?

ArrayDeque<Character> sQueue = new ArrayDeque<Character>();
ArrayDeque<Character> tQueue = new ArrayDeque<Character>();

if (sQueue.size() != tQueue.size()) return false;

while (!sQueue.isEmpty()) {
   if (sQueue.removeLast() != tQueue.removeLast()) {
       return false;
   }
}

return true;

Question Context: for people who use Leetcode Backspace String Compare

Also, is the original Equals for ArrayDeque just checking thememory pointer variable? this does not seem to work.

Resource: Why doesn't ArrayDeque override equals() and hashCode()?

Answer 1

Your code probably would work if you don't use != but instead this:

    if (!Objects.equals(sQueue.removeLast(), tQueue.removeLast())) {

There's one issue with your code - it removes all contents of the queue. To prevent that, besides using toArray() as suggested in one of the comments, you an use an Iterator; Deque mandates that it returns "the elements in this deque in proper sequence":

ArrayDeque<Character> sQueue = new ArrayDeque<Character>();
ArrayDeque<Character> tQueue = new ArrayDeque<Character>();

// shortcut - that's fine
if (sQueue.size() != tQueue.size()) return false;

Iterator<Character> sIterator = sQueue.iterator();
Iterator<Character> tIterator = sQueue.iterator();

while (sIterator.hasNext()) {
    // tIterator.hasNext() will also be true
    if (!Objects.equals(sIterator.next(), tIterator.next())) {
        return false;
    }
}
// sIterator and tIterator are both exhausted so all elements are equal
return true;

You can do it without the length check, by making two changes:

1. Replace while (sIterator.hasNext()) { with while (sIterator.hasNext() && tIterator.hasNext()) { - keep looping until at least one of the iterators is exhausted.
2. Replace the final return true; with return sIterator.hasNext() == tIterator.hasNext(); - return true only if both iterators are exhausted.