solve speeking iterator #284 in java

Author: anishLearnsToCode

README.md

@@ -231,7 +231,7 @@
 | 280  | 🔒 [Wiggle Sort](https://leetcode.com/problems/wiggle-sort)                                                                                               |                                                                                                                                                                                                                                  |                                                                                                                                   |
 | 281  | 🔒 [Zigzag Iterator](https://leetcode.com/problems/zigzag-iterator)                                                                                       |                                                                                                                                                                                                                                  |                                                                                                                                   |
 | 283  | [Move Zeroes](https://leetcode.com/problems/move-zeroes)                                                                                                  |                                                               [![Java](assets/java.png)](src/MoveZeros.java) [![Python](assets/python.png)](python/move_zeroes.py)                                                               |                                                                                                                                   |
-| 284  | [Peeking Iterator](https://leetcode.com/problems/peeking-iterator)                                                                                        |                                                                                                                                                                                                                                  |                                                                                                                                   |
+| 284  | [Peeking Iterator](https://leetcode.com/problems/peeking-iterator)                                                                                        |                                                                                       [![Java](assets/java.png)](src/PeekingIterator.java)                                                                                       |                                                                                                                                   |
 | 285  | 🔒 [Inorder Successor in BST](https://leetcode.com/problems/inorder-successor-in-bst)                                                                     |                                                                                                                                                                                                                                  |                                                                                                                                   |
 | 286  | 🔒 [Walls and Gates](https://leetcode.com/problems/walls-and-gates)                                                                                       |                                                                                                                                                                                                                                  |                                                                                                                                   |
 | 287  | [Find the Duplicate Number](https://leetcode.com/problems/find-the-duplicate-number)                                                                      |                                                                                                                                                                                                                                  |                                                                                                                                   |

src/PeekingIterator.java

@@ -0,0 +1,37 @@
+// https://leetcode.com/problems/peeking-iterator
+// T: O(N)
+// S: O(N)
+
+import java.util.Iterator;
+
+public class PeekingIterator implements Iterator<Integer> {
+    final private Iterator<Integer> iterator;
+    int next;
+    boolean hasNext;
+
+    public PeekingIterator(Iterator<Integer> iterator) {
+        this.iterator = iterator;
+        hasNext = iterator.hasNext();
+        next = iterator.hasNext() ? iterator.next() : 0;
+    }
+
+    // Returns the next element in the iteration without advancing the iterator.
+    public Integer peek() {
+        return next;
+    }
+
+    // hasNext() and next() should behave the same as in the Iterator interface.
+    // Override them if needed.
+    @Override
+    public Integer next() {
+        int result = next;
+        hasNext = iterator.hasNext();
+        next = iterator.hasNext() ? iterator.next() : 0;
+        return result;
+    }
+
+    @Override
+    public boolean hasNext() {
+        return hasNext;
+    }
+}