leetcode 284. Peeking Iterator

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.

// 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 {
vector<int>num;
int k = 0;
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.
num = nums;
}
// Returns the next element in the iteration without advancing the iterator.
int peek() {
return num[k];
}
// hasNext() and next() should behave the same as in the Iterator interface.
// Override them if needed.
int next() {
return num[k++];
}
bool hasNext() const {
return k < num.size();
}
};


accept