Package g0201_0300.s0284_peeking_iterator

Class PeekingIterator

java.lang.Object
g0201_0300.s0284_peeking_iterator.PeekingIterator
All Implemented Interfaces:
java.util.Iterator<java.lang.Integer>
public class PeekingIterator extends java.lang.Object implements java.util.Iterator<java.lang.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?

  • Constructor Summary

    Constructors
    Constructor
    Description
    PeekingIterator(java.util.Iterator<java.lang.Integer> iterator)
     

  • Method Summary

    Modifier and Type
    Method
    Description
    boolean
    hasNext()
     
    java.lang.Integer
    next()
     
    java.lang.Integer
    peek()
     

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    Methods inherited from interface java.util.Iterator

    forEachRemaining, remove

  • Constructor Details

    • PeekingIterator

      public PeekingIterator(java.util.Iterator<java.lang.Integer> iterator)

  • Method Details

    • peek

      public java.lang.Integer peek()

    • next

      public java.lang.Integer next()
      Specified by:
      next in interface java.util.Iterator<java.lang.Integer>

    • hasNext

      public boolean hasNext()
      Specified by:
      hasNext in interface java.util.Iterator<java.lang.Integer>