solves sum of unique elements

Author: anishLearnsToCode

Diff for: README.md

@@ -427,7 +427,7 @@
 | 1732 | [Find the Highest Altitude](https://leetcode.com/problems/find-the-highest-altitude)                                                                      |                                                             [![Java](assets/java.png)](src/FindTheHighestAltitude.java)                                                              |                                                                                                                                   |
 | 1736 | [Latest Time by Replacing Hidden Digits](https://leetcode.com/problems/latest-time-by-replacing-hidden-digits)                                            |                                                        [![Java](assets/java.png)](src/LatestTimeByReplacingHiddenDigits.java)                                                        |                                                                                                                                   |
 | 1742 | [Maximum Number of Balls in a Box](https://leetcode.com/problems/maximum-number-of-balls-in-a-box)                                                        |                                                           [![Java](assets/java.png)](src/MaximumNumberOfBallsInABox.java)                                                            |                                                                                                                                   |
-| 1748 | [Sum of Unique Elements](https://leetcode.com/problems/sum-of-unique-elements)                                                                            |                                                                                                                                                                                      |                                                                                                                                   |
+| 1748 | [Sum of Unique Elements](https://leetcode.com/problems/sum-of-unique-elements)                                                                            |                                                                 [![Java](assets/java.png)](src/SumOfUniqueElements.java)                                                                 |                                                                                                                                   |
 | 1752 | [Check if Array Is Sorted and Rotated](https://leetcode.com/problems/check-if-array-is-sorted-and-rotated)                                                |                                                                                                                                                                                      |                                                                                                                                   |
 | 1758 | [Minimum Changes To Make Alternating Binary String](https://leetcode.com/problems/minimum-changes-to-make-alternating-binary-string)                      |                                                                                                                                                                                      |                                                                                                                                   |
 | 1763 | [Longest Nice Substring](https://leetcode.com/problems/longest-nice-substring)                                                                            |                                                                                                                                                                                      |                                                                                                                                   |

Diff for: src/SumOfUniqueElements.java

@@ -0,0 +1,37 @@
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Set;
+
+public class SumOfUniqueElements {
+    public int sumOfUnique(int[] nums) {
+        final Set<Integer> uniqueElements = uniqueElements(nums);
+        return sum(uniqueElements);
+    }
+
+    private Set<Integer> uniqueElements(int[] array) {
+        final Map<Integer, Integer> frequencies = getFrequencies(array);
+        final Set<Integer> set = new HashSet<>();
+        for (Map.Entry<Integer, Integer> entry : frequencies.entrySet()) {
+            if (entry.getValue() == 1) set.add(entry.getKey());
+        }
+        return set;
+    }
+
+    private Map<Integer, Integer> getFrequencies(int[] array) {
+        final Map<Integer, Integer> frequencies = new HashMap<>();
+        for (int element : array) {
+            frequencies.put(element, frequencies.getOrDefault(element, 0) + 1);
+        }
+        return frequencies;
+    }
+
+    private int sum(Collection<Integer> collection) {
+        int sum = 0;
+        for (int element : collection) {
+            sum += element;
+        }
+        return sum;
+    }
+}