LeetCode *** 284. Peeking Iterator

题目：

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.

分析：

无。

パナマ与最近的一些政策与国民。我对于这个国家毫无感情。希望自己能够快点离开。

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:
bool saved=false;
int num;
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.
saved=false;
}

// Returns the next element in the iteration without advancing the iterator.
int peek() {
if(saved)return num;
else {
num=next();
saved=true;
return num;
}
}

// hasNext() and next() should behave the same as in the Iterator interface.
// Override them if needed.
int next() {
if(saved){
saved=false;
return num;
}
else return Iterator::next();
}

bool hasNext() const {
return saved||Iterator::hasNext();
}
};