leetcode 284. Peeking Iterator | 284. 顶端迭代器（给 iterator 添加 peek 方法）

末蓝、 2022-10-12 04:19 154阅读 0赞

## 题目 ##

[https://leetcode.com/problems/peeking-iterator/][https_leetcode.com_problems_peeking-iterator]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NpbmF0XzQyNDgzMzQx_size_1_color_FFFFFF_t_70]

## 题解 ##

一句话解释题意：标准的 iter 接口不包含 peek 功能，本题希望你能够增加这个功能。

// Java Iterator interface reference:
    // https://docs.oracle.com/javase/8/docs/api/java/util/Iterator.html
    
    class PeekingIterator implements Iterator<Integer> { 
        Iterator<Integer> iter;
        Integer num;
    
        public PeekingIterator(Iterator<Integer> iterator) { 
            // initialize any member here.
            iter = iterator;
            if (iterator.hasNext())
                num = iterator.next();
        }
    
        // Returns the next element in the iteration without advancing the iterator.
        public Integer peek() { 
            return num;
        }
    
        // hasNext() and next() should behave the same as in the Iterator interface.
        // Override them if needed.
        @Override
        public Integer next() { 
            Integer ret = num;
            if (iter.hasNext())
                num = iter.next();
            else
                num = null;
            return ret;
        }
    
        @Override
        public boolean hasNext() { 
            return num != null;
        }
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NpbmF0XzQyNDgzMzQx_size_16_color_FFFFFF_t_70]

[https_leetcode.com_problems_peeking-iterator]: https://leetcode.com/problems/peeking-iterator/
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NpbmF0XzQyNDgzMzQx_size_1_color_FFFFFF_t_70]: /images/20221005/1d9b30861cea4548ae4e0061b4c7aab7.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NpbmF0XzQyNDgzMzQx_size_16_color_FFFFFF_t_70]: /images/20221005/55e399c45c6e49b1a3194eeef046b9b5.png