284. Peeking Iterator

Given an Iterator class interface with methods:next()andhasNext(), design and implement a PeekingIterator that support thepeek()operation -- it essentially peek() at the element that will be returned by the next call to next().

Here is an example. Assume that the iterator is initialized to the beginning of the list:[1, 2, 3].

Callnext()gets you 1, the first element in the list.

Now you callpeek()and it returns 2, the next element. Callingnext()after thatstillreturn 2.

You callnext()the final time and it returns 3, the last element. CallinghasNext()after that should return false.

Follow up: How would you extend your design to be generic and work with all types, not just integer?

S：c++ copy constructor && inheritance

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) {    
    }

    // 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();
    }

};