LinkedList reverse method added, Queue changed to java.util in binary tree

Author: Badri Paudel

.gitignore

@@ -1,2 +1,4 @@
 .idea/
 out/
+#*.iml
+#**/*.iml match all .iml file in all directory and sub-directory.

data_structure_algorithm.iml

@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<module type="JAVA_MODULE" version="4">
+  <component name="NewModuleRootManager" inherit-compiler-output="true">
+    <exclude-output />
+    <content url="file://$MODULE_DIR$">
+      <sourceFolder url="file://$MODULE_DIR$/src" isTestSource="false" />
+    </content>
+    <orderEntry type="inheritedJdk" />
+    <orderEntry type="sourceFolder" forTests="false" />
+  </component>
+</module>

src/com/cs/dsa/binarytrees/BinaryTree.java

@@ -1,6 +1,7 @@
 package com.cs.dsa.binarytrees;
 
-import sun.misc.Queue;
+import java.util.LinkedList;
+import java.util.Queue;
 
 /*
  * Created By Badri Paudel on 02/08/2022 - Software Developer at Threadcode Technologies
@@ -62,21 +63,21 @@ nodes are visited and moving up (or down)
 
     protected void searchBFS() throws InterruptedException {
         Node rNode = rootNode; // access to the root node
-        Queue queue = new Queue(); // queue to store visited nodes
+        Queue queue =  new LinkedList(); // queue to store visited nodes
         if (rNode != null) {
-            queue.enqueue(rNode); // visited add to the queue
+            queue.add(rNode); // visited add to the queue
             // visit all by looping
             System.out.print("Visiting values ::: ");
             while (!queue.isEmpty()) {
-                rNode = (Node) queue.dequeue(); // pop that element off
+                rNode = (Node) queue.poll(); // pop that element off
                 System.out.print(" " + rNode.element);
                 // VisIts left node and puts it into the queue
                 if (rNode.left != null) {
-                    queue.enqueue(rNode.left);
+                    queue.add(rNode.left);
                 }
                 // visits right node and put it in the queue
                 if (rNode.right != null) {
-                    queue.enqueue(rNode.right);
+                    queue.add(rNode.right);
                 }
             }
             System.out.println(" = Travelling BFS finished");

src/com/cs/dsa/linkedlist/LinkedList.java

@@ -156,6 +156,40 @@ public Node removeNodeAtIndex(int index) {
         return nodeToBeRemoved;
     }
 
+    // Reverse the LL: O(n), in-place
+    /**
+     * Swap head and tail and change the direction of the pointer (pointing to the next)
+     * Visualize by drawing a diagram, it should be clear.
+     * Main idea is to maintain pointer to prev, after and navigate accordingly until
+     * all the pointers(next) are flipped back.
+     */
+    public void reverse() {
+        if(length == 0) {
+            System.out.println("LL is empty, so can't be reversed.");
+            return;
+        }
+        if(length == 1) {
+            System.out.println("There is only one node in the LL, already reversed.");
+            return;
+        }
+        // swap the head and tail
+        Node temp = head;
+        head = tail;
+        tail = temp;
+
+        Node prev = null;
+        Node after;
+
+        // change the direction of the pointer
+        for(int i=0; i< length; i++) {
+            after = temp.next;
+            temp.next = prev;
+            prev = temp;
+            temp = after;
+        }
+        System.out.println("LL is now reversed.");
+    }
+
     public Node getHead() {
         System.out.println("Currently head is pointing at node : " + head + " with value: " + head.value);
         return this.head;
@@ -205,5 +239,9 @@ public static void main(String[] args) {
 
         linkedList.getHead();
         linkedList.getTail();
+        linkedList.printList();
+
+        linkedList.reverse();
+        linkedList.printList();
     }
 }