Max Iterator

Author: Deepak Malik

README.md

@@ -34,7 +34,7 @@ Implementation of Algorithms in Java, Most of these names are picked up from Gee
 	- [X] [Hopping Iterator](../master/src/com/deepak/algorithms/Iterators/HoppingIterator.java)
 	- [ ] InOrder Iterator
 	- [X] [LevelOrder Iterator](../master/src/com/deepak/algorithms/Iterators/LevelOrderIterator.java)
-	- [ ] MaxIterator Iterator
+	- [X] [MaxIterator Iterator](../master/src/com/deepak/algorithms/Iterators/MaxIterator.java)
 	- [ ] MultiIterator Iterator
 	- [ ] Peek Iterator
 	- [ ] PreOrder Iterator

src/com/deepak/algorithms/Iterators/HoppingIterator.java

@@ -25,14 +25,6 @@
  * If the original iterator returns: [1, 2, 3, 4, 5] in order, then the hopping
  * iterator will return [1, 5] in order when the hop value is 3.
  * 
- * Methods expected to be implemented:
- *  
- * public class HoppingIterator<T> implements Iterator<T> {
- * 		public HoppingIterator(Iterator<T> iterator, int numHops) {...}
- * 		public boolean hasNext() {...}
- * 		public T next() {...}
- * }
- * 
  * </br>
  * 
  * @author Deepak

src/com/deepak/algorithms/Iterators/MaxIterator.java

@@ -0,0 +1,84 @@
+/**
+ * Algorithms-In-Java
+ * MaxIterator.java
+ */
+package com.deepak.algorithms.Iterators;
+
+import java.util.Comparator;
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+
+/**
+ * <br> Problem Statement :
+ * 
+ * Implement a max iterator i.e. it always returns the next item in the list
+ * bigger than the last item returned.
+ * 
+ * </br>
+ * 
+ * @author Deepak
+ */
+public class MaxIterator<T> implements Iterator<T> {
+
+	/* Iterator and Comparator */
+	private final Iterator<T> iterator;
+	private final Comparator<T> comparator;
+	/* Variables to store last item and next item */
+	private T lastItem;
+	private T nextItem;
+
+	/**
+	 * Constructor
+	 * 
+	 * @param iterator
+	 * @param comparator
+	 */
+	public MaxIterator(Iterator<T> iterator, Comparator<T> comparator) {
+		this.iterator = iterator;
+		this.comparator = comparator;
+	}
+
+	/**
+	 * Method to check if next element exists
+	 */
+	@Override
+	public boolean hasNext() {
+		/* If next item is not null, return true */
+		if (nextItem != null) {
+			return true;
+		}
+		/* Else go through the collection and find the next bigger element */
+		while (nextItem == null && iterator.hasNext()) {
+			T item = iterator.next();
+			if (lastItem == null || comparator.compare(item, lastItem) > 0) {
+				nextItem = item;
+			}
+		}
+		/* Return true if exists */
+		return nextItem != null;
+	}
+
+	/**
+	 * Method to find next element
+	 */
+	@Override
+	public T next() {
+		/* If next element doesn't exists, throw exception */
+		if (!hasNext()) {
+			throw new NoSuchElementException("No element found in collection!!");
+		}
+		/* Else update the last item found */
+		lastItem = nextItem;
+		nextItem = null;
+		return lastItem;
+	}
+
+	/**
+	 * Method to remove the element
+	 */
+	@Override
+	public void remove() {
+		throw new UnsupportedOperationException("Remove not supported!!");
+	}
+
+}

test/com/deepak/algorithms/Iterators/MaxIterator_Test.java

@@ -0,0 +1,43 @@
+/**
+ * Algorithms-in-Java
+ * MaxIterator_Test.java
+ */
+package com.deepak.algorithms.Iterators;
+
+import java.util.Arrays;
+import java.util.Comparator;
+import java.util.List;
+import java.util.NoSuchElementException;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * Test cases for max iterator
+ * 
+ * @author Deepak
+ */
+public class MaxIterator_Test {
+
+	/**
+	 * Test case to validate max iterator
+	 */
+	@Test(expected=NoSuchElementException.class)
+	public void testMaxIterator() {
+		List<Integer> integerList = Arrays.asList(2, 1, 4, 9, 5);
+		MaxIterator<Integer> maxIterator = new MaxIterator<>(integerList.iterator(), 
+				new Comparator<Integer>() {
+			@Override
+			public int compare(Integer a, Integer b) {
+				return a - b;
+			}
+		});
+		Assert.assertTrue(maxIterator.hasNext());
+		Assert.assertTrue(maxIterator.next() == 2);
+		Assert.assertTrue(maxIterator.next() == 4);
+		Assert.assertTrue(maxIterator.next() == 9);
+		Assert.assertFalse(maxIterator.hasNext());
+		Assert.assertTrue(maxIterator.next() == 9);
+	}
+
+}