Share my C++ solution,easy to understand


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    // 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 {
    
    private:
        int nextElement;
        bool isHasNext;
    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.
    	    this->next();
    	}
    
        // Returns the next element in the iteration without advancing the iterator.
    	int peek() {
            return nextElement;
    	}
    
    	// hasNext() and next() should behave the same as in the Iterator interface.
    	// Override them if needed.
    	int next() {
    	    int ret = nextElement;
    	    
    	    if (Iterator::hasNext())
    	    {
    	        isHasNext = true;
    	        nextElement = Iterator::next();
    	    }
    	    else
            {
                isHasNext = false;
            }
            
            return ret;
    	}
    
    	bool hasNext() const {
    	    return isHasNext;
    	}
    };

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