Create Peeking Iterator.java

varunu28 · web-flow · commit 19c28e78e77a · 2018-04-02T10:24:30.000-07:00
diff --git a/Medium/Peeking Iterator.java b/Medium/Peeking Iterator.java
@@ -0,0 +1,47 @@
+// Java Iterator interface reference:
+// https://docs.oracle.com/javase/8/docs/api/java/util/Iterator.html
+import java.util.NoSuchElementException;
+
+class PeekingIterator implements Iterator<Integer> {
+
+    private Integer next;
+    private Iterator<Integer> iter;
+    private boolean noNextElement = false;
+    
+    public PeekingIterator(Iterator<Integer> iterator) {
+        // initialize any member here.
+        iter = iterator;
+        moveIterator();
+    }
+
+    // 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() {
+        if (noNextElement) {
+            throw new NoSuchElementException();
+        }
+        Integer val = next;
+        moveIterator();
+        return val;   
+    }
+
+    @Override
+    public boolean hasNext() {
+        return !noNextElement;
+    }
+    
+    public void moveIterator() {
+        if (iter.hasNext()) {
+            next = iter.next();
+        }
+        else {
+            noNextElement = true;
+        }
+    }
+}
