# 284. Peeking Iterator

Peeking Iterator - LeetCode

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 iterator iterator.
int next() Returns the next element in the array and moves the pointer to the next element.
boolean hasNext() Returns true 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 and peek are valid.
At most 1000 calls will be made to next, hasNext, and peek.
``````

• code
``````class PeekingIterator implements Iterator<Integer> {
private Iterator<Integer> iter;
private Integer peek = null;
public PeekingIterator(Iterator<Integer> iterator) {
iter = iterator;
}

public Integer peek() {
if (peek == null){
peek = iter.next();
}
return peek;
}

@Override
public Integer next() {
if (peek != null){
int toReturn = peek;
peek = null;
}
return iter.next();
}

@Override
public boolean hasNext() {
return peek != null || iter.hasNext();
}
}
``````
• code
``````class PeekingIterator:
def __init__(self, iterator):
self._next = iterator.next()
self._iterator = iterator

def peek(self):
return self._next

def next(self):
to_return = self._next
self._next = None
if self._iterator.hasNext():
self._next = self._iterator.next()