Added Sum of Unique Elements.java

Author: varunu28

Easy/Sum of Unique Elements.java

@@ -0,0 +1,10 @@
+import java.util.Map.Entry;
+
+class Solution {
+  public int sumOfUnique(int[] nums) {
+    return Arrays.stream(nums).boxed()
+        .collect(Collectors.groupingBy(Function.identity(), HashMap::new, Collectors.counting()))
+        .entrySet().stream().filter(e -> e.getValue().equals(1L)).map(
+            Entry::getKey).reduce(0, Integer::sum);
+  }
+}