LeetCode OJ：Peeking Iterator（peeking 迭代器）

 1 // Below is the interface for Iterator, which is already defined for you.
 2 // **DO NOT** modify the interface for Iterator.
 3 class Iterator {
 4     struct Data;
 5     Data* data;
 6 public:
 7     Iterator(const vector<int>& nums);
 8     Iterator(const Iterator& iter);
 9     virtual ~Iterator();
10     // Returns the next element in the iteration.
11     int next();
12     // Returns true if the iteration has more elements.
13     bool hasNext() const;
14 };
15 
16 
17 class PeekingIterator : public Iterator {
18 public:
19     PeekingIterator(const vector<int>& nums) : Iterator(nums) {
20         // Initialize any member here.
21         // **DO NOT** save a copy of nums and manipulate it directly.
22         // You should only use the Iterator interface methods.
23         this->next();
24     }
25 
26     // Returns the next element in the iteration without advancing the iterator.
27     int peek() {
28         return nextVal;
29     }
30 
31     // hasNext() and next() should behave the same as in the Iterator interface.
32     // Override them if needed.
33     int next() {
34         int ret = nextVal;
35         if(Iterator::hasNext()){
36             bNext = true;
37             nextVal = Iterator::next();
38         }else{
39             bNext = false;
40         }
41         return ret;
42     }
43 
44     bool hasNext() const {
45         return bNext;
46     }
47 private:
48     bool bNext;
49     int nextVal;
50 };