2021.10.5打卡

思路：C++中已实现方法next和hasnext，主要实现peek方法，。使用flag标识迭代器是否有剩余元素，使用nextElement存储迭代器下一个元素。

class PeekingIterator : public Iterator {
public:
	PeekingIterator(const vector& 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.
	    flag = Iterator::hasNext();
        if(flag)
            nextElement = Iterator::next();
	}
	
    // Returns the next element in the iteration without advancing the iterator.
	int peek() {
        return nextElement;
	}
	
	// hasNext() and next() should behave the same as in the Iterator interface.
	// Override them if needed.
	int next() {
	    int ret = nextElement;
        flag = Iterator::hasNext();
        if(flag)
            nextElement = Iterator::next();
        return ret;
	}
	
	bool hasNext() const {
	    return flag;
	}

    bool flag;
    int nextElement;
};