284.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 {
    bool hasPeeked;
    int peekElement;
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.
        peekElement = 0;
        hasPeeked = false;
    }

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

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

    bool hasNext() const {
        if (hasPeeked) return true;
        return Iterator::hasNext();
    }
};

/*
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() {
        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();
    }
};
*/