[Leetcode] Peeking Iterator, Solution

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[/i] return 2.You call

next()

the final time and it returns 3, the last element. Calling

hasNext()

after that should return false.[Thoughts]链表的一道设计题。next其实在这里就是获取头元素的值，并移动到下一个元素。peek在这里就是返回当前元素的值。

[code]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:  class PeekingIterator : public Iterator {
16:  public:
17:       PeekingIterator(const vector<int>& nums) : Iterator(nums) {
18:         // Initialize any member here.
19:         // **DO NOT** save a copy of nums and manipulate it directly.
20:         // You should only use the Iterator interface methods.
21:         this->length = nums.size();
22:         this->nums = &nums;
23:       }
24:       // Returns the next element in the iteration without advancing the iterator.
25:       int peek() {
26:         if(currentIndex < length) {
27:           return (*this->nums)[currentIndex];
28:         }
29:         return -1;
30:       }
31:       // hasNext() and next() should behave the same as in the Iterator interface.
32:       // Override them if needed.
33:       int next() {
34:         if(currentIndex < length) {
35:           currentIndex ++;
36:           return (*this->nums)[currentIndex-1];
37:         }
38:         return -1;
39:       }
40:       bool hasNext() const {
41:         return currentIndex < length;
42:       }
43:  private:
44:    int currentIndex = 0;
45:    int length = 0;
46:    const vector<int>* nums = NULL;
47:  };

github：[/b]https://github.com/codingtmd/leetcode/blob/master/src/Peeking_Iterator.cpp