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// Java Iterator interface reference:
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// https://docs.oracle.com/javase/8/docs/api/java/util/Iterator.html
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class PeekingIterator implements Iterator<Integer> {
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  Queue<Integer> q;
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  public PeekingIterator(Iterator<Integer> iterator) {
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    // initialize any member here.
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    q = new LinkedList<>();
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    while (iterator.hasNext()) q.add(iterator.next());
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  }
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  // Returns the next element in the iteration without advancing the iterator.
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  public Integer peek() {
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    return q.peek();
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  }
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  // hasNext() and next() should behave the same as in the Iterator interface.
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  // Override them if needed.
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  @Override
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  public Integer next() {
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    return q.remove();
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  }
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  @Override
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  public boolean hasNext() {
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    return q.size() != 0;
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  }
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}