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