diff --git a/DIRECTORY.md b/DIRECTORY.md
index aebc14852b14..5b3ee19d0eee 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -8,6 +8,7 @@
             * [IIRFilter](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/audiofilters/IIRFilter.java)
           * backtracking
             * [Combination](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/backtracking/Combination.java)
+            * [FloodFill](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/backtracking/FloodFill.java)
             * [KnightsTour](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/backtracking/KnightsTour.java)
             * [NQueens](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/backtracking/NQueens.java)
             * [Permutation](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/backtracking/Permutation.java)
@@ -93,7 +94,6 @@
               * [MergeSortedArrayList](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/lists/MergeSortedArrayList.java)
               * [MergeSortedSinglyLinkedList](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/lists/MergeSortedSinglyLinkedList.java)
               * [RandomNode](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/lists/RandomNode.java)
-              * [RemoveDuplicateNodes](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/lists/RemoveDuplicateNodes.java)
               * [SearchSinglyLinkedListRecursion](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/lists/SearchSinglyLinkedListRecursion.java)
               * [SinglyLinkedList](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/lists/SinglyLinkedList.java)
             * queues
@@ -108,15 +108,18 @@
               * [DecimalToAnyUsingStack](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/stacks/DecimalToAnyUsingStack.java)
               * [DuplicateBrackets](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/stacks/DuplicateBrackets.java)
               * [InfixToPostfix](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/stacks/InfixToPostfix.java)
+              * [LargestRectangle](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/stacks/LargestRectangle.java)
               * [MaximumMinimumWindow](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/stacks/MaximumMinimumWindow.java)
               * [NextGraterElement](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/stacks/NextGraterElement.java)
               * [NextSmallerElement](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/stacks/NextSmallerElement.java)
               * [NodeStack](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/stacks/NodeStack.java)
+              * [PostfixToInfix](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/stacks/PostfixToInfix.java)
               * [ReverseStack](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/stacks/ReverseStack.java)
               * [StackArray](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/stacks/StackArray.java)
               * [StackArrayList](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/stacks/StackArrayList.java)
               * [StackOfLinkedList](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/stacks/StackOfLinkedList.java)
             * trees
+              * [AVLSimple](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/trees/AVLSimple.java)
               * [AVLTree](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/trees/AVLTree.java)
               * [BinaryTree](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/trees/BinaryTree.java)
               * [BSTIterative](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/trees/BSTIterative.java)
@@ -160,12 +163,12 @@
             * [BruteForceKnapsack](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/BruteForceKnapsack.java)
             * [CatalanNumber](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/CatalanNumber.java)
             * [CoinChange](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/CoinChange.java)
+            * [CountFriendsPairing](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/CountFriendsPairing.java)
             * [DiceThrow](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/DiceThrow.java)
             * [DyanamicProgrammingKnapsack](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/DyanamicProgrammingKnapsack.java)
             * [EditDistance](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/EditDistance.java)
             * [EggDropping](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/EggDropping.java)
             * [Fibonacci](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/Fibonacci.java)
-            * [FloodFill](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/FloodFill.java)
             * [FordFulkerson](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/FordFulkerson.java)
             * [KadaneAlgorithm](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/KadaneAlgorithm.java)
             * [Knapsack](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/Knapsack.java)
@@ -182,12 +185,14 @@
             * [MemoizationTechniqueKnapsack](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/MemoizationTechniqueKnapsack.java)
             * [MinimumPathSum](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/MinimumPathSum.java)
             * [MinimumSumPartition](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/MinimumSumPartition.java)
+            * [NewManShanksPrime](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/NewManShanksPrime.java)
             * [PalindromicPartitioning](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/PalindromicPartitioning.java)
             * [RegexMatching](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/RegexMatching.java)
             * [RodCutting](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/RodCutting.java)
             * [ShortestCommonSupersequenceLength](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/ShortestCommonSupersequenceLength.java)
             * [SubsetSum](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/SubsetSum.java)
             * [Sum Of Subset](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/Sum_Of_Subset.java)
+            * [UniquePaths](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/UniquePaths.java)
             * [WineProblem](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/WineProblem.java)
           * maths
             * [AbsoluteMax](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/maths/AbsoluteMax.java)
@@ -217,6 +222,7 @@
             * [FFTBluestein](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/maths/FFTBluestein.java)
             * [FibonacciJavaStreams](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/maths/FibonacciJavaStreams.java)
             * [FibonacciNumber](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/maths/FibonacciNumber.java)
+            * [FindKthNumber](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/maths/FindKthNumber.java)
             * [FindMax](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/maths/FindMax.java)
             * [FindMaxRecursion](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/maths/FindMaxRecursion.java)
             * [FindMin](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/maths/FindMin.java)
@@ -407,29 +413,35 @@
             * [Upper](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/strings/Upper.java)
             * [WordLadder](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/strings/WordLadder.java)
   * test
-    * backtracking
-      * [CombinationTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/backtracking/CombinationTest.java)
-      * [FloodFillTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/backtracking/FloodFillTest.java)
-      * [PermutationTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/backtracking/PermutationTest.java)
-    * maths
-      * [FFTTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/FFTTest.java)
-      * [GaussianTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/GaussianTest.java)
-      * [KaprekarNumbersTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/KaprekarNumbersTest.java)
-      * [PascalTriangleTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/PascalTriangleTest.java)
-      * [PronicNumberTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/PronicNumberTest.java)
-      * [SquareRootwithBabylonianMethodTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/SquareRootwithBabylonianMethodTest.java)
-    * others
-      * [ArrayLeftRotationTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/ArrayLeftRotationTest.java)
-      * [BestFitCPUTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/BestFitCPUTest.java)
-      * [FirstFitCPUTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/FirstFitCPUTest.java)
-      * [KadaneAlogrithmTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/KadaneAlogrithmTest.java)
-      * [LinkList Sort test](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/LinkList_Sort_test.java)
-      * [NewManShanksPrimeTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/NewManShanksPrimeTest.java)
-      * [NextFitTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/NextFitTest.java)
-      * [UniquePathsTests](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/UniquePathsTests.java)
-      * [WorstFitCPUTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/WorstFitCPUTest.java)
-    * searches
-      * [QuickSelectTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/searches/QuickSelectTest.java)
-    * strings
-      * [AlphabeticalTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/strings/AlphabeticalTest.java)
-      * [PangramTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/strings/PangramTest.java)
+          * backtracking
+            * [CombinationTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/backtracking/CombinationTest.java)
+            * [FloodFillTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/backtracking/FloodFillTest.java)
+            * [PermutationTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/backtracking/PermutationTest.java)
+          * maths
+            * [ArmstrongTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/ArmstrongTest.java)
+            * [FFTTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/FFTTest.java)
+            * [GaussianTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/GaussianTest.java)
+            * [KaprekarNumbersTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/KaprekarNumbersTest.java)
+            * [PascalTriangleTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/PascalTriangleTest.java)
+            * [PronicNumberTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/PronicNumberTest.java)
+            * [SquareRootwithBabylonianMethodTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/SquareRootwithBabylonianMethodTest.java)
+          * others
+            * [ArrayLeftRotationTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/ArrayLeftRotationTest.java)
+            * [BestFitCPUTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/BestFitCPUTest.java)
+            * [CountFriendsPairingTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/CountFriendsPairingTest.java)
+            * [FirstFitCPUTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/FirstFitCPUTest.java)
+            * [KadaneAlogrithmTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/KadaneAlogrithmTest.java)
+            * [LinkList Sort test](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/LinkList_Sort_test.java)
+            * [NewManShanksPrimeTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/NewManShanksPrimeTest.java)
+            * [NextFitTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/NextFitTest.java)
+            * [UniquePathsTests](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/UniquePathsTests.java)
+            * [WorstFitCPUTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/WorstFitCPUTest.java)
+          * searches
+            * [QuickSelectTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/searches/QuickSelectTest.java)
+          * strings
+            * [AlphabeticalTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/strings/AlphabeticalTest.java)
+            * [AnagramsTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/strings/AnagramsTest.java)
+            * [CharacterSameTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/strings/CharacterSameTest.java)
+            * [PalindromeTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/strings/PalindromeTest.java)
+            * [PangramTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/strings/PangramTest.java)
+            * [UpperTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/strings/UpperTest.java)
diff --git a/pom.xml b/pom.xml
index 571c14060f33..56af5539986b 100644
--- a/pom.xml
+++ b/pom.xml
@@ -7,10 +7,12 @@
     <artifactId>Java</artifactId>
     <version>1.0-SNAPSHOT</version>
     <packaging>jar</packaging>
+
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <maven.compiler.source>17</maven.compiler.source>
         <maven.compiler.target>17</maven.compiler.target>
+        <assertj.version>3.22.0</assertj.version>
     </properties>
 
     <dependencyManagement>
@@ -31,6 +33,11 @@
             <artifactId>junit-jupiter</artifactId>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+        </dependency>
     </dependencies>
 
     <build>
diff --git a/src/main/java/com/thealgorithms/maths/Armstrong.java b/src/main/java/com/thealgorithms/maths/Armstrong.java
index df65ba750b01..fa1198ceaea3 100644
--- a/src/main/java/com/thealgorithms/maths/Armstrong.java
+++ b/src/main/java/com/thealgorithms/maths/Armstrong.java
@@ -4,18 +4,11 @@
  * An Armstrong number is equal to the sum of the cubes of its digits. For
  * example, 370 is an Armstrong number because 3*3*3 + 7*7*7 + 0*0*0 = 370. An
  * Armstrong number is often called Narcissistic number.
+ *
+ * @author Vivek
  */
 public class Armstrong {
 
-    public static void main(String[] args) {
-        assert (isArmStrong(0));
-        assert (isArmStrong(1));
-        assert (isArmStrong(153));
-        assert (isArmStrong(1634));
-        assert (isArmStrong(371));
-        assert (!isArmStrong(200));
-    }
-
     /**
      * Checks whether a given number is an armstrong number or not.
      *
@@ -23,24 +16,14 @@ public static void main(String[] args) {
      * @return {@code true} if given number is armstrong number, {@code false}
      * otherwise
      */
-    private static boolean isArmStrong(int number) {
-        int sum = 0;
-        int temp = number;
-        int numberOfDigits = 0;
-        while (temp != 0) {
-            numberOfDigits++;
-            temp /= 10;
-        }
-        temp = number;
-        /* copy number again */
-        while (number > 0) {
-            int remainder = number % 10;
-            int power = 1;
-            for (int i = 1; i <= numberOfDigits; power *= remainder, ++i)
-        ;
-            sum = sum + power;
-            number /= 10;
+    public boolean isArmstrong(int number) {
+        long sum = 0;
+        long number2 = number;
+        while (number2 > 0) {
+            long mod = number2 % 10;
+            sum += Math.pow(mod, 3);
+            number2 /= 10;
         }
-        return sum == temp;
+        return sum == number;
     }
-}
+}
\ No newline at end of file
diff --git a/src/test/java/com/thealgorithms/maths/ArmstrongTest.java b/src/test/java/com/thealgorithms/maths/ArmstrongTest.java
new file mode 100644
index 000000000000..a833e41044f7
--- /dev/null
+++ b/src/test/java/com/thealgorithms/maths/ArmstrongTest.java
@@ -0,0 +1,23 @@
+package com.thealgorithms.maths;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * @author Vivek
+ * @since 15/03/22
+ */
+class ArmstrongTest {
+
+    @Test
+    void testIsArmstrong() {
+        Armstrong armstrong = new Armstrong();
+        assertThat(armstrong.isArmstrong(0)).isTrue();
+        assertThat(armstrong.isArmstrong(1)).isTrue();
+        assertThat(armstrong.isArmstrong(153)).isTrue();
+        assertThat(armstrong.isArmstrong(371)).isTrue();
+        assertThat(armstrong.isArmstrong(1634)).isFalse();
+        assertThat(armstrong.isArmstrong(200)).isFalse();
+    }
+}