leetcode题解日练--2016.7.16

日练三题，冰冻三尺非一日之寒。

今日题目：1、顶端迭代器；2、完美平方数；3、根节点到叶节点的加法。

今日摘录：

人生是一场旅程。我们经历了几次轮回，才换来这个旅程。而这个旅程很短，因此不妨大胆一些，不妨大胆一些去爱一个人，去攀一座山，去追一个梦……有很多事我都不明白。但我相信一件事。上天让我们来到这个世上，就是为了让我们创造奇迹 ——-《大鱼海棠》

284. Peeking Iterator | Difficulty: Medium

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.

题意：实现一个类

思路：
1、利用复制构造函数

// 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.

    }

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

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

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

结果：4ms

2、

// 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