284 (1) add solution

stevencooks · stevencooks · commit c5e5f49f3b7b · 2015-09-30T21:33:39.000-04:00
diff --git a/src/_284_PeekingIterator/Solution.java b/src/_284_PeekingIterator/Solution.java
@@ -0,0 +1,60 @@
+/**
+ * Time : O() ; Space: O()
+ * @tag : Design
+ * @by  : Steven Cooks
+ * @date: Sep 30, 2015
+ ***************************************************************************
+ * Description:
+ * 
+ * Given an Iterator class interface with methods: next() and hasNext(), 
+ * design and implement a PeekingIterator that support the peek() operation 
+ * -- it essentially peek() at the element that will be returned by the next 
+ * call to next().
+ * 
+ ***************************************************************************
+ * {@link https://leetcode.com/problems/peeking-iterator/ }
+ */
+package _284_PeekingIterator;
+
+import java.util.Iterator;
+
+/** see test {@link _284_PeekingIterator.SolutionTest } */
+public class Solution implements Iterator<Integer> {
+    
+    private Integer cache;
+    
+    private Iterator<Integer> _iter;
+    
+    public Solution(Iterator<Integer> iterator) {
+        // initialize any member here.
+        cache = null;
+        _iter = iterator;
+    }
+
+    // Returns the next element in the iteration without advancing the iterator.
+    public Integer peek() {
+        if (cache == null) {
+            cache = _iter.next();
+        }
+        return cache;
+    }
+
+    // hasNext() and next() should behave the same as in the Iterator interface.
+    // Override them if needed.
+    @Override
+    public Integer next() {
+        if (cache != null) {
+            Integer next = cache;
+            cache = null;
+            return next;
+        } else {
+            return _iter.next();
+        }
+    }
+
+    @Override
+    public boolean hasNext() {
+        return _iter.hasNext() || cache != null;
+    }
+
+}
