Add aykrieger: First Non-Duplicate

Author: aykrieger

README.md

@@ -184,7 +184,9 @@ HackerRank assigns their problems a difficulty rating (Easy, Medium, Hard, Exper
 
 - K-diff Pairs in an Array (Medium) [Problem](https://leetcode.com/problems/k-diff-pairs-in-an-array/) | [Solution](https://github.com/aykrieger/coding-exercises/blob/master/src/main/java/leetcode/KDiffPairsInAnArray.java)
 
+## aykrieger (1 Problem)
 
+-  First Non-Duplicate [Solution](https://github.com/aykrieger/coding-exercises/blob/master/src/main/java/aykrieger/FirstNonDuplicate.java)
 
 ## Contributing
 

pom.xml

@@ -13,6 +13,13 @@
       <artifactId>commons-lang3</artifactId>
       <version>3.7</version>
     </dependency>
+    <!-- https://mvnrepository.com/artifact/org.junit.jupiter/junit-jupiter-api -->
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter-api</artifactId>
+      <version>5.8.2</version>
+      <scope>test</scope>
+    </dependency>
   </dependencies>
 
   <properties>

src/main/java/aykrieger/FirstNonDuplicate.java

@@ -0,0 +1,20 @@
+package aykrieger;
+
+import java.util.LinkedHashSet;
+
+public class FirstNonDuplicate {
+
+  private LinkedHashSet<Integer> linkedSet = new LinkedHashSet<>();
+
+  public void add(int number) {
+    if (!linkedSet.contains(number)) {
+      linkedSet.add(number);
+    } else {
+      linkedSet.remove(number);
+    }
+  }
+
+  public int firstNonDuplicate() {
+    return linkedSet.isEmpty() ? -1 : linkedSet.iterator().next();
+  }
+}

src/test/java/aykrieger/FirstNonDuplicateTest.java

@@ -0,0 +1,27 @@
+package aykrieger;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Test class for {@link FirstNonDuplicate}
+ */
+public class FirstNonDuplicateTest {
+
+  @Test
+  public void testFirstNonDuplicate() {
+    FirstNonDuplicate firstNonDuplicate = new FirstNonDuplicate();
+    firstNonDuplicate.add(10);
+    firstNonDuplicate.add(11);
+    firstNonDuplicate.add(12);
+    assertEquals(10, firstNonDuplicate.firstNonDuplicate());
+    firstNonDuplicate.add(10);
+    assertEquals(11, firstNonDuplicate.firstNonDuplicate());
+    firstNonDuplicate.add(11);
+    firstNonDuplicate.add(12);
+    assertEquals(-1, firstNonDuplicate.firstNonDuplicate());
+  }
+
+
+}