[leetcode] 284. Peeking Iterator 解题报告

题目链接: https://leetcode.com/problems/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.

Hint:

1. Think of "looking ahead". You want to cache the next element.Show More Hint 

Follow up: How would you extend your design to be generic and work with all types, not just integer?

思路: 感觉也没什么意思的一题, 废话了一堆, 最后就是两个指针判断一下. 如果要适用所有的类型就用泛型.

代码如下:

// 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.
	    it = nums.begin();
	    itEnd = nums.end();
	}

    // Returns the next element in the iteration without advancing the iterator.
	int peek() {
        return *it;
	}

	// hasNext() and next() should behave the same as in the Iterator interface.
	// Override them if needed.
	int next() {
	    return *(it++);
	}

	bool hasNext() const {
	    if(it == itEnd)
	        return false;
	    return true;
	}
private:
    vector<int>::const_iterator it, itEnd;
};