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peeking-iterator.py
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# Time: O(1) per peek(), next(), hasNext()
# Space: O(1)
class PeekingIterator(object):
def __init__(self, iterator):
"""
Initialize your data structure here.
:type iterator: Iterator
"""
self.iterator = iterator
self.val_ = None
self.has_next_ = iterator.hasNext()
self.has_peeked_ = False
def peek(self):
"""
Returns the next element in the iteration without advancing the iterator.
:rtype: int
"""
if not self.has_peeked_:
self.has_peeked_ = True
self.val_ = self.iterator.next()
return self.val_
def next(self):
"""
:rtype: int
"""
self.val_ = self.peek()
self.has_peeked_ = False
self.has_next_ = self.iterator.hasNext()
return self.val_
def hasNext(self):
"""
:rtype: bool
"""
return self.has_next_