peeking-iterator.cc

// Peeking Iterator

// 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 {
  bool f;
  int x;
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.
    f = false;
  }

  // Returns the next element in the iteration without advancing the iterator.
  int peek() {
    if (! f) {
      f = true;
      x = Iterator::next();
    }
    return x;
  }

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

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