284 Peeking Iterator .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.
        if (Iterator::hasNext()) {
            nxt = Iterator::next();
            hasNow = true;
        } else {
            hasNow = false;
        }
    }

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

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

    bool hasNext() const {
        return hasNow;
    }
private:
    int nxt;
    bool hasNow;
};