Merge branch 'master' into median_new_algo

Author: Hardvan

DIRECTORY.md

@@ -868,6 +868,7 @@
               * [QueueByTwoStacksTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/queues/QueueByTwoStacksTest.java)
               * [QueueTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/queues/QueueTest.java)
             * stacks
+              * [NodeStackTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/stacks/NodeStackTest.java)
               * [StackArrayListTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/stacks/StackArrayListTest.java)
               * [StackArrayTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/stacks/StackArrayTest.java)
               * [StackOfLinkedListTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/stacks/StackOfLinkedListTest.java)

src/main/java/com/thealgorithms/datastructures/lists/RotateSinglyLinkedLists.java

@@ -1,11 +1,43 @@
 package com.thealgorithms.datastructures.lists;
 
 /**
- * Rotate a list
- * @author Bama Charan Chhandogi (https://github.com/BamaCharanChhandogi)
+ * The RotateSinglyLinkedLists class provides a method to rotate a singly linked list
+ * to the right by a specified number of positions.
+ * <p>
+ * In a right rotation by `k` steps, each node in the list moves `k` positions to the right.
+ * Nodes that are rotated off the end of the list are placed back at the beginning.
+ * </p>
+ * <p>
+ * Example:
+ * Given linked list: 1 -> 2 -> 3 -> 4 -> 5 and k = 2, the output will be:
+ * 4 -> 5 -> 1 -> 2 -> 3.
+ * </p>
+ * <p>
+ * Edge Cases:
+ * <ul>
+ *   <li>If the list is empty, returns null.</li>
+ *   <li>If `k` is 0 or a multiple of the list length, the list remains unchanged.</li>
+ * </ul>
+ * </p>
+ * <p>
+ * Complexity:
+ * <ul>
+ *   <li>Time Complexity: O(n), where n is the number of nodes in the linked list.</li>
+ *   <li>Space Complexity: O(1), as we only use a constant amount of additional space.</li>
+ * </ul>
+ * </p>
+ *
+ * Author: Bama Charan Chhandogi (https://github.com/BamaCharanChhandogi)
  */
-
 public class RotateSinglyLinkedLists {
+
+    /**
+     * Rotates a singly linked list to the right by `k` positions.
+     *
+     * @param head The head node of the singly linked list.
+     * @param k The number of positions to rotate the list to the right.
+     * @return The head of the rotated linked list.
+     */
     public Node rotateRight(Node head, int k) {
         if (head == null || head.next == null || k == 0) {
             return head;

src/main/java/com/thealgorithms/datastructures/queues/GenericArrayListQueue.java

@@ -4,43 +4,46 @@
 import java.util.List;
 
 /**
- * This class implements a GenericArrayListQueue.
+ * This class implements a GenericArrayListQueue, a queue data structure that
+ * holds elements of any type specified at runtime, allowing flexibility in the type
+ * of elements it stores.
  *
- * A GenericArrayListQueue data structure functions the same as any
- * specific-typed queue. The GenericArrayListQueue holds elements of types
- * to-be-specified at runtime. The elements that are added first are the first
- * to be removed (FIFO). New elements are added to the back/rear of the queue.
+ * <p>The GenericArrayListQueue operates on a First-In-First-Out (FIFO) basis, where
+ * elements added first are the first to be removed. New elements are added to the back
+ * (or rear) of the queue, while removal of elements occurs from the front.
+ *
+ * @param <T> The type of elements held in this queue.
  */
 public class GenericArrayListQueue<T> {
 
     /**
-     * The generic List for the queue. T is the generic element type.
+     * A list that stores the queue's elements in insertion order.
      */
     private final List<T> elementList = new ArrayList<>();
 
     /**
      * Checks if the queue is empty.
      *
-     * @return True if the queue is empty, false otherwise.
+     * @return {@code true} if the queue has no elements; {@code false} otherwise.
      */
-    private boolean isEmpty() {
+    public boolean isEmpty() {
         return elementList.isEmpty();
     }
 
     /**
-     * Returns the element at the front of the queue without removing it.
+     * Retrieves, but does not remove, the element at the front of the queue.
      *
-     * @return The element at the front of the queue, or null if the queue is empty.
+     * @return The element at the front of the queue, or {@code null} if the queue is empty.
      */
     public T peek() {
         return isEmpty() ? null : elementList.getFirst();
     }
 
     /**
-     * Inserts an element of type T to the back of the queue.
+     * Inserts an element at the back of the queue.
      *
-     * @param element the element to be added to the queue.
-     * @return True if the element was added successfully.
+     * @param element The element to be added to the queue.
+     * @return {@code true} if the element was successfully added.
      */
     public boolean add(T element) {
         return elementList.add(element);
@@ -49,7 +52,7 @@ public boolean add(T element) {
     /**
      * Retrieves and removes the element at the front of the queue.
      *
-     * @return The element removed from the front of the queue, or null if the queue is empty.
+     * @return The element removed from the front of the queue, or {@code null} if the queue is empty.
      */
     public T poll() {
         return isEmpty() ? null : elementList.removeFirst();

src/main/java/com/thealgorithms/datastructures/stacks/NodeStack.java

@@ -1,161 +1,109 @@
 package com.thealgorithms.datastructures.stacks;
 
 /**
- * Implementation of a stack using nodes. Unlimited size, no arraylist.
+ * A stack implementation using linked nodes, supporting unlimited size without an ArrayList.
  *
- * @author Kyler Smith, 2017
+ * <p>Each node in the stack contains data of generic type {@code Item}, along with references
+ * to the next and previous nodes, supporting typical stack operations.
+ *
+ * <p>The stack follows a Last-In-First-Out (LIFO) order where elements added last are
+ * removed first. Supported operations include push, pop, and peek.
+ *
+ * @param <Item> the type of elements held in this stack
  */
 public class NodeStack<Item> {
 
     /**
-     * Entry point for the program.
+     * Node class representing each element in the stack.
      */
-    public static void main(String[] args) {
-        NodeStack<Integer> stack = new NodeStack<Integer>();
-
-        stack.push(3);
-        stack.push(4);
-        stack.push(5);
-        System.out.println("Testing :");
-        stack.print(); // prints : 5 4 3
+    private class Node {
+        Item data;
+        Node previous;
 
-        Integer x = stack.pop(); // x = 5
-        stack.push(1);
-        stack.push(8);
-        Integer y = stack.peek(); // y = 8
-        System.out.println("Testing :");
-        stack.print(); // prints : 8 1 4 3
-
-        System.out.println("Testing :");
-        System.out.println("x : " + x);
-        System.out.println("y : " + y);
+        Node(Item data) {
+            this.data = data;
+            this.previous = null;
+        }
     }
 
-    /**
-     * Information each node should contain.
-     *
-     * @value data : information of the value in the node
-     * @value head : the head of the stack
-     * @value next : the next value from this node
-     * @value previous : the last value from this node
-     * @value size : size of the stack
-     */
-    private Item data;
-
-    private static NodeStack<?> head;
-    private NodeStack<?> previous;
-    private static int size = 0;
+    private Node head; // Top node in the stack
+    private int size; // Number of elements in the stack
 
     /**
-     * Constructors for the NodeStack.
+     * Constructs an empty NodeStack.
      */
     public NodeStack() {
-    }
-
-    private NodeStack(Item item) {
-        this.data = item;
+        head = null;
+        size = 0;
     }
 
     /**
-     * Put a value onto the stack.
+     * Pushes an item onto the stack.
      *
-     * @param item : value to be put on the stack.
+     * @param item the item to be pushed onto the stack
      */
     public void push(Item item) {
-        NodeStack<Item> newNs = new NodeStack<Item>(item);
-
-        if (this.isEmpty()) {
-            NodeStack.setHead(new NodeStack<>(item));
-            newNs.setNext(null);
-            newNs.setPrevious(null);
-        } else {
-            newNs.setPrevious(NodeStack.head);
-            NodeStack.head.setNext(newNs);
-            NodeStack.setHead(newNs);
-        }
-
-        NodeStack.setSize(NodeStack.getSize() + 1);
+        Node newNode = new Node(item);
+        newNode.previous = head;
+        head = newNode;
+        size++;
     }
 
     /**
-     * Value to be taken off the stack.
+     * Removes and returns the item at the top of the stack.
      *
-     * @return item : value that is returned.
+     * @return the item at the top of the stack, or {@code null} if the stack is empty
+     * @throws IllegalStateException if the stack is empty
      */
     public Item pop() {
-        Item item = (Item) NodeStack.head.getData();
-
-        NodeStack.setHead(NodeStack.head.getPrevious());
-        NodeStack.head.setNext(null);
-
-        NodeStack.setSize(NodeStack.getSize() - 1);
-
-        return item;
+        if (isEmpty()) {
+            throw new IllegalStateException("Cannot pop from an empty stack.");
+        }
+        Item data = head.data;
+        head = head.previous;
+        size--;
+        return data;
     }
 
     /**
-     * Value that is next to be taken off the stack.
+     * Returns the item at the top of the stack without removing it.
      *
-     * @return item : the next value that would be popped off the stack.
+     * @return the item at the top of the stack, or {@code null} if the stack is empty
+     * @throws IllegalStateException if the stack is empty
      */
     public Item peek() {
-        return (Item) NodeStack.head.getData();
+        if (isEmpty()) {
+            throw new IllegalStateException("Cannot peek from an empty stack.");
+        }
+        return head.data;
     }
 
     /**
-     * If the stack is empty or there is a value in.
+     * Checks whether the stack is empty.
      *
-     * @return boolean : whether or not the stack has anything in it.
+     * @return {@code true} if the stack has no elements, {@code false} otherwise
      */
     public boolean isEmpty() {
-        return NodeStack.getSize() == 0;
+        return head == null;
     }
 
     /**
-     * Returns the size of the stack.
+     * Returns the number of elements currently in the stack.
      *
-     * @return int : number of values in the stack.
+     * @return the size of the stack
      */
     public int size() {
-        return NodeStack.getSize();
+        return size;
     }
 
     /**
-     * Print the contents of the stack in the following format.
-     *
-     * <p>
-     * x <- head (next out) y z <- tail (first in) . . .
+     * Prints the contents of the stack from top to bottom.
      */
     public void print() {
-        for (NodeStack<?> n = NodeStack.head; n != null; n = n.previous) {
-            System.out.println(n.getData().toString());
+        Node current = head;
+        while (current != null) {
+            System.out.println(current.data);
+            current = current.previous;
         }
     }
-
-    private static void setHead(NodeStack<?> ns) {
-        NodeStack.head = ns;
-    }
-
-    private void setNext(NodeStack<?> next) {
-    }
-
-    private NodeStack<?> getPrevious() {
-        return previous;
-    }
-
-    private void setPrevious(NodeStack<?> previous) {
-        this.previous = previous;
-    }
-
-    private static int getSize() {
-        return size;
-    }
-
-    private static void setSize(int size) {
-        NodeStack.size = size;
-    }
-
-    private Item getData() {
-        return this.data;
-    }
 }