Add select random tree node algorithm (#2906)

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
Co-authored-by: Andrii Siriak <siryaka@gmail.com>

DIRECTORY.md

@@ -133,6 +133,7 @@
               * [PrintTopViewofTree](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/trees/PrintTopViewofTree.java)
               * [RedBlackBST](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/trees/RedBlackBST.java)
               * [SegmentTree](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/trees/SegmentTree.java)
+              * [TreeRandomNode](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/trees/TreeRandomNode.java)
               * [TreeTraversal](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/trees/TreeTraversal.java)
               * [TrieImp](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/trees/TrieImp.java)
               * [ValidBSTOrNot](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/trees/ValidBSTOrNot.java)
@@ -369,6 +370,7 @@
             * [GnomeSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/GnomeSort.java)
             * [HeapSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/HeapSort.java)
             * [InsertionSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/InsertionSort.java)
+            * [LinkList Sort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/LinkList_Sort.java)
             * [MergeSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/MergeSort.java)
             * [MergeSortNoExtraSpace](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/MergeSortNoExtraSpace.java)
             * [MergeSortRecursive](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/MergeSortRecursive.java)
@@ -404,14 +406,12 @@
             * [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
-    * java
-      * com
-        * thealgorithms
           * maths
             * [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)
           * others
             * [ArrayLeftRotationTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/ArrayLeftRotationTest.java)
+            * [LinkList Sort test](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/LinkList_Sort_test.java)
           * searches
             * [QuickSelectTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/searches/QuickSelectTest.java)

src/main/java/com/thealgorithms/datastructures/trees/TreeRandomNode.java

@@ -0,0 +1,93 @@
+/* Author : Suraj Kumar
+  Github : https://github.com/skmodi649
+ */
+
+/* PROBLEM DESCRIPTION :
+  There is a Binary Search Tree given, and we are supposed to find a random node in the given binary tree.
+ */
+
+/* ALGORITHM :
+  Step 1: START
+  Step 2: First create a binary tree using the steps mentioned in the first approach
+  Step 3: Now use a method inOrder() that takes a node as input parameter to traverse through the
+          binary tree in inorder fashion as also store the values in a ArrayList simultaneously.
+  Step 4: Now define a method getrandom() that takes a node as input parameter, in this first call
+          the inOrder() method to store the values in the arraylist, then find the size of the binary tree and now just generate a random number between 0 to n-1.
+  Step 5: After generating the number display the value of the ArrayList at the generated index
+  Step 6: STOP
+ */
+
+
+import java.util.ArrayList;
+
+// Using auxiliary array to find the random node in a given binary tree
+class Node {
+    int item;
+    Node left, right;
+
+    public Node(int key) {
+        item = key;
+        left = right = null;
+    }
+}
+
+public class TreeRandomNode {
+
+    // Using an arraylist to store the inorder traversal of the given binary tree
+    static ArrayList<Integer> list = new ArrayList<>();
+    // root of Tree
+    Node root;
+
+    TreeRandomNode() {
+        root = null;
+    }
+
+    // Now lets find the inorder traversal of the given binary tree
+    static void inOrder(Node node) {
+        if (node == null)
+            return;
+
+        // traverse the left child
+        inOrder(node.left);
+
+        list.add(node.item);
+        // traverse the right child
+        inOrder(node.right);
+    }
+
+    public void getrandom(Node val)
+    {
+        inOrder(val);
+        // getting the count of node of the binary tree
+        int n = list.size();
+        int min = 0;
+        int max = n - 1;
+        //Generate random int value from 0 to n-1
+        int b = (int)(Math.random()*(max-min+1)+min);
+        // displaying the value at the generated index
+        int random = list.get(b);
+        System.out.println("Random Node : " + random);
+
+    }
+}
+
+
+/* Explanation of the Approach :
+  (a) Form the required binary tree
+  (b) Now use the inOrder() method to get the nodes in inOrder fashion and also store them in the given arraylist 'list'
+  (c) Using the getRandom() method generate a random number between 0 to n-1, then get the value at the generated random number
+      from the arraylist using get() method and finally display the result.
+ */
+
+
+/* OUTPUT :
+  First output :
+  Random Node : 15
+  Second output :
+  Random Node : 99
+ */
+
+/* Time Complexity : O(n)
+  Auxiliary Space Complexity : O(1)
+ */
+