Create MiddleOfLinkedList.java

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

@@ -0,0 +1,84 @@
+package com.thealgorithms.datastructures.lists;
+
+/**
+ * Class to find the middle node of a singly-linked list.
+ */
+public class MiddleOfLinkedList {
+
+    /**
+     * Definition for singly-linked list node.
+     * Package-private class so it can be used internally.
+     */
+    static class ListNode {
+        int val; // Value stored in the node
+        ListNode next; // Pointer to the next node
+
+        /**
+         * Constructor to initialize a node with a value.
+         *
+         * @param val Value to store in the node.
+         */
+        ListNode(int val) {
+            this.val = val;
+            this.next = null;
+        }
+    }
+
+    /**
+     * Finds the middle node of a singly linked list.
+     * If there are two middle nodes, returns the second one.
+     *
+     * @param head Head node of the linked list.
+     * @return Middle node of the list.
+     */
+    public ListNode middleNode(ListNode head) {
+        if (head == null) {
+            return head;
+        }
+
+        ListNode slow = head; // moves one step at a time
+        ListNode fast = head; // moves two steps at a time
+
+        while (fast != null && fast.next != null) {
+            slow = slow.next; // move slow by one node
+            fast = fast.next.next; // move fast by two nodes
+        }
+
+        return slow;
+    }
+
+    /**
+     * Helper method to create a linked list from an array.
+     *
+     * @param values Array of integer values.
+     * @return Head node of the created linked list.
+     */
+    public static ListNode createList(int[] values) {
+        if (values.length == 0) {
+            return null;
+        }
+
+        ListNode head = new ListNode(values[0]);
+        ListNode current = head;
+
+        for (int i = 1; i < values.length; i++) {
+            current.next = new ListNode(values[i]);
+            current = current.next;
+        }
+
+        return head;
+    }
+
+    /**
+     * Helper method to print the linked list starting from any node.
+     *
+     * @param node Starting node to print from.
+     */
+    public static void printList(ListNode node) {
+        while (node != null) {
+            System.out.print(node.val + " "); // print current node value
+            node = node.next; // move to next node
+        }
+        System.out.println();
+    }
+}