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Design an iterator that supports the peek operation on a list in addition to the hasNext and the next operations.

Implement the PeekingIterator class:

  • PeekingIterator(int[] nums) Initializes the object with the given integer array nums.
  • int next() Returns the next element in the array and moves the pointer to the next element.
  • bool hasNext() Returns true if there are still elements in the array.
  • int peek() Returns the next element in the array without moving the pointer.

 

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?

// Java Iterator interface reference: // https://docs.oracle.com/javase/8/docs/api/java/util/Iterator.html class PeekingIterator implements Iterator<Integer> { public PeekingIterator(Iterator<Integer> iterator) { // initialize any member here. } // Returns the next element in the iteration without advancing the iterator. public Integer peek() { } // hasNext() and next() should behave the same as in the Iterator interface. // Override them if needed. @Override public Integer next() { } @Override public boolean hasNext() { } }