Package g0201_0300.s0284_peeking_iterator

Class PeekingIterator

  • All Implemented Interfaces:
    Iterator<Integer>
    public class PeekingIterator
extends Object
implements Iterator<Integer>
    284 - Peeking Iterator.

    Medium

    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.

    Follow up: How would you extend your design to be generic and work with all types, not just integer?