#284

Peeking Iterator

specialist · 740 · lc medium +31 · 61.3% accepted · 1,909 likes · top 61%

Description

Extend an existing iterator with a peek operation alongside hasNext and next.

Implement the PeekingIterator class:

- PeekingIterator(Iterator<int> nums) Wraps the given integer iterator iterator.

- int next() Returns the next element and advances the iterator.

- boolean hasNext() Returns true if more elements remain.

- int peek() Returns the next element without advancing the iterator.

Note: Each language may have a different implementation of the constructor and Iterator, but they all support the int next() and boolean hasNext() functions.

Example 1:

Input

["PeekingIterator", "next", "peek", "next", "next", "hasNext"]

[[[1, 2, 3]], [], [], [], [], []]

Output

[null, 1, 2, 2, 3, false]

Example 2:

Explanation

PeekingIterator peekingIterator = new PeekingIterator([1, 2, 3]); // [1,2,3]

peekingIterator.next(); // return 1, the pointer moves to the next element [1,2,3].

peekingIterator.peek(); // return 2, the pointer does not move [1,2,3].

peekingIterator.next(); // return 2, the pointer moves to the next element [1,2,3]

peekingIterator.next(); // return 3, the pointer moves to the next element [1,2,3]

peekingIterator.hasNext(); // return False

Code

# 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
        """
        

    def peek(self):
        """
        Returns the next element in the iteration without advancing the iterator.
        :rtype: int
        """
        

    def next(self):
        """
        :rtype: int
        """
        

    def hasNext(self):
        """
        :rtype: bool
        """
        

# 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].

# 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
        """
        

    def peek(self):
        """
        Returns the next element in the iteration without advancing the iterator.
        :rtype: int
        """
        

    def next(self):
        """
        :rtype: int
        """
        

    def hasNext(self):
        """
        :rtype: bool
        """
        

# 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].