coded + unit tested

Author: Ram swaroop

src/me/ramswaroop/arrays/DuplicatesInArrayWithinKDistance.java

@@ -0,0 +1,47 @@
+package me.ramswaroop.arrays;
+
+import java.util.Arrays;
+import java.util.HashSet;
+
+/**
+ * Created by IntelliJ IDEA.
+ *
+ * @author: ramswaroop
+ * @date: 10/18/15
+ * @time: 8:40 PM
+ */
+public class DuplicatesInArrayWithinKDistance {
+
+    /**
+     * Finds duplicates in an unsorted array {@param a} which are
+     * only k distance apart from each other.
+     *
+     * @param a
+     * @param k
+     * @return
+     */
+    public static int[] findDuplicatesInArrayWithinKDistance(int[] a, int k) {
+        int index = 0;
+        int[] duplicates = new int[a.length];
+
+        HashSet<Integer> hashSet = new HashSet<>();
+
+        for (int i = 0; i < a.length; i++) {
+            if (hashSet.contains(a[i])) {
+                duplicates[index++] = a[i];
+            } else {
+                hashSet.add(a[i]);
+            }
+
+            if (i >= k) {
+                hashSet.remove(a[i - k]);
+            }
+        }
+
+        return Arrays.copyOf(duplicates, index);
+    }
+
+    public static void main(String a[]) {
+        System.out.println(Arrays.toString(findDuplicatesInArrayWithinKDistance(new int[]{1, 2, 8, 1, 3, 4, 5, 6, 6, 7}, 3)));
+    }
+}