284.cpp

// .cpp
// Below is the interface for Iterator, which is already defined for you.
// **DO NOT** modify the interface for Iterator.
class Iterator {
  struct Data;
  Data *data;

public:
  Iterator(const vector<int> &nums);
  Iterator(const Iterator &iter);
  virtual ~Iterator();
  // Returns the next element in the iteration.
  int next();
  // Returns true if the iteration has more elements.
  bool hasNext() const;
};

class PeekingIterator : public Iterator {
public:
  PeekingIterator(const vector<int> &nums) : Iterator(nums) {
    // Initialize any member here.
    // **DO NOT** save a copy of nums and manipulate it directly.
    // You should only use the Iterator interface methods.
  }

  // Returns the next element in the iteration without advancing the iterator.
  int peek() { return Iterator(*this).next(); }

  // hasNext() and next() should behave the same as in the Iterator interface.
  // Override them if needed.
  int next() { return Iterator::next(); }

  bool hasNext() const { return Iterator::hasNext(); }
};