Design an iterator that supports the peek
operation on an existing iterator in addition to the hasNext
and the next
operations.
Implement the PeekingIterator
class:
-
PeekingIterator(Iterator<int> nums)
Initializes the object with the given integer iteratoriterator
. -
int next()
Returns the next element in the array and moves the pointer to the next element. -
boolean hasNext()
Returnstrue
if there are still elements in the array. -
int peek()
Returns the next element in the array without moving the pointer.
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]
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
Constraints:
-
1 <= nums.length <= 1000
-
1 <= nums[i] <= 1000
- All the calls to
next
andpeek
are valid. - At most
1000
calls will be made tonext
,hasNext
, andpeek
.
Follow up: How would you extend your design to be generic and work with all types, not just integer?SOLUTION:
# 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):
self.itr = iterator
self.curr = None
def peek(self):
if self.curr != None:
return self.curr
self.curr = self.itr.next()
return self.curr
def next(self):
if self.curr != None:
val = self.curr
self.curr = None
return val
return self.itr.next()
def hasNext(self):
return self.curr != None or self.itr.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].
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