给定一个迭代器类的接口，接口包含两个方法： next() 和 hasNext()。设计并实现一个支持 peek() 操作的顶端迭代器 -- 其本质就是把原本应由 next() 方法返回的元素 peek() 出来。
示例:
假设迭代器被初始化为列表[1,2,3]。 调用next()返回 1，得到列表中的第一个元素。 现在调用peek()返回 2，下一个元素。在此之后调用next()仍然返回 2。 最后一次调用next()返回 3，末尾元素。在此之后调用hasNext()应该返回 false。
进阶：你将如何拓展你的设计？使之变得通用化，从而适应所有的类型，而不只是整数型？
# Below is the interface for Iterator, which is already defined for you.
#
# class Iterator:
# def __init__(self, nums):
# """
# Initializes an iterator object to the beginning of a list.
# :type nums: List[int]
# """
#
# def hasNext(self):
# """
# Returns true if the iteration has more elements.
# :rtype: bool
# """
#
# def next(self):
# """
# Returns the next element in the iteration.
# :rtype: int
# """
class PeekingIterator:
def __init__(self, iterator):
"""
Initialize your data structure here.
:type iterator: Iterator
"""
self.iterator = iterator
self.has_peeked = False
self.peeked_element = None
def peek(self):
"""
Returns the next element in the iteration without advancing the iterator.
:rtype: int
"""
if not self.has_peeked:
self.peeked_element = self.iterator.next()
self.has_peeked = True
return self.peeked_element
def next(self):
"""
:rtype: int
"""
if not self.has_peeked:
return self.iterator.next()
result = self.peeked_element
self.has_peeked = False
self.peeked_element = None
return result
def hasNext(self):
"""
:rtype: bool
"""
return self.has_peeked or self.iterator.hasNext()
# Your PeekingIterator object will be instantiated and called as such:
# iter = PeekingIterator(Iterator(nums))
# while iter.hasNext():
# val = iter.peek() # Get the next element but not advance the iterator.
# iter.next() # Should return the same value as [val].// Java Iterator interface reference:
// https://docs.oracle.com/javase/8/docs/api/java/util/Iterator.html
class PeekingIterator implements Iterator<Integer> {
private Iterator<Integer> iterator;
private boolean hasPeeked;
private Integer peekedElement;
public PeekingIterator(Iterator<Integer> iterator) {
// initialize any member here.
this.iterator = iterator;
}
// Returns the next element in the iteration without advancing the iterator.
public Integer peek() {
if (!hasPeeked) {
peekedElement = iterator.next();
hasPeeked = true;
}
return peekedElement;
}
// hasNext() and next() should behave the same as in the Iterator interface.
// Override them if needed.
@Override
public Integer next() {
if (!hasPeeked) {
return iterator.next();
}
Integer result = peekedElement;
hasPeeked = false;
peekedElement = null;
return result;
}
@Override
public boolean hasNext() {
return hasPeeked || iterator.hasNext();
}
}