1.题目要求实现一个窥探的功能，正常的迭代器，可以输出当前值和使用next指向下一个值。而题目要求我们输出下一个值，但是不移动指针。
2.当使用peek时，利用this指针重建了一个迭代器，在这个这个新的迭代器中执行next操作并返回值，即可不影响原来的迭代器。
Given an Iterator class interface with methods: next() and hasNext(), design and implement a PeekingIterator that support the peek() 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].
Call next() gets you 1, the first element in the list.
Now you call peek() and it returns 2, the next element. Calling next() after that still return 2.
You call next() the final time and it returns 3, the last element. Calling hasNext() after that should return false.
AC代码：
// 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.
}
// Returns the next element in the iteration without advancing the iterator.
int peek() {
if(hasNext())
{
Iterator same(*this);//复制一个迭代器
return same.next();//输入这个迭代器的下一个值
}
}
// 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();
}
};
