Add StackUsingLinkedList.java for #6715

Author: Kamal1023

src/main/java/com/thealgorithms/stacks/StackUsingLinkedList.java

@@ -0,0 +1,69 @@
+/**
+ * Stack implementation using singly linked list.
+ * Supports push, pop, peek, isEmpty, and size operations in O(1) time.
+ * 
+ * Issue: #6715
+ * Author: @Kamal1023
+ */
+public class StackUsingLinkedList<T> {
+    private Node<T> top;
+    private int size;
+
+    // Inner Node class
+    private static class Node<T> {
+        T data;
+        Node<T> next;
+        Node(T data) {
+            this.data = data;
+            this.next = null;
+        }
+    }
+
+    //Pushes an element onto the stack 
+    public void push(T data) {
+        Node<T> node = new Node<>(data);
+        node.next = top;
+        top = node;
+        size++;
+    }
+
+    // Removes and returns the top element of the stack 
+    public T pop() {
+        if (isEmpty()) throw new RuntimeException("Stack is empty");
+        T data = top.data;
+        top = top.next;
+        size--;
+        return data;
+    }
+
+    /** Returns the top element without removing it */
+    public T peek() {
+        if (isEmpty()) throw new RuntimeException("Stack is empty");
+        return top.data;
+    }
+
+    /** Checks if the stack is empty */
+    public boolean isEmpty() {
+        return top == null;
+    }
+
+    //Returns the number of elements in the stack 
+    public int size() {
+        return size;
+    }
+
+    // Demo/test for StackUsingLinkedList 
+    public static void main(String[] args) {
+        StackUsingLinkedList<Integer> stack = new StackUsingLinkedList<>();
+        stack.push(10);
+        stack.push(20);
+        stack.push(30);
+
+        System.out.println("Top: " + stack.peek()); // 30
+        System.out.println("Size: " + stack.size()); // 3
+
+        while (!stack.isEmpty()) {
+            System.out.println("Pop: " + stack.pop());
+        }
+    }
+}