Add solution #284

Author: JoshCrozier

README.md

@@ -226,6 +226,7 @@
 279|[Perfect Squares](./0279-perfect-squares.js)|Medium|
 282|[Expression Add Operators](./0282-expression-add-operators.js)|Hard|
 283|[Move Zeroes](./0283-move-zeroes.js)|Easy|
+284|[Peeking Iterator](./0284-peeking-iterator.js)|Medium|
 287|[Find the Duplicate Number](./0287-find-the-duplicate-number.js)|Medium|
 289|[Game of Life](./0289-game-of-life.js)|Medium|
 290|[Word Pattern](./0290-word-pattern.js)|Easy|

solutions/0284-peeking-iterator.js

@@ -0,0 +1,49 @@
+/**
+ * 284. Peeking Iterator
+ * https://leetcode.com/problems/peeking-iterator/
+ * Difficulty: 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.
+ */
+
+/**
+ * @param {Iterator} iterator
+ */
+var PeekingIterator = function(iterator) {
+  this.iterator = iterator;
+  this.peekValue = iterator.next();
+};
+
+/**
+ * @return {number}
+ */
+PeekingIterator.prototype.peek = function() {
+  return this.peekValue;
+};
+
+/**
+ * @return {number}
+ */
+PeekingIterator.prototype.next = function() {
+  const next = this.peekValue;
+  this.peekValue = this.iterator.next();
+  return next;
+};
+
+/**
+ * @return {boolean}
+ */
+PeekingIterator.prototype.hasNext = function() {
+  return this.peekValue > 0;
+};