From 2f056c53785b2affae465121afca662dfdda410a Mon Sep 17 00:00:00 2001
From: Suraj Kumar <76468931+skmodi649@users.noreply.github.com>
Date: Wed, 5 Jan 2022 18:53:09 +0530
Subject: [PATCH] chore(Java): add random node in a binary tree (#659)

---
 algorithms/Java/README.md                   |   1 +
 algorithms/Java/trees/tree-random-node.java | 109 ++++++++++++++++++++
 2 files changed, 110 insertions(+)
 create mode 100644 algorithms/Java/trees/tree-random-node.java

diff --git a/algorithms/Java/README.md b/algorithms/Java/README.md
index f5357f3d..7c3329aa 100644
--- a/algorithms/Java/README.md
+++ b/algorithms/Java/README.md
@@ -96,6 +96,7 @@
 - [Zig-Zag Traversal of a Tree](trees/zig-zag-traversal.java)
 - [Min Heap](trees/MinHeap.java)
 - [Check Tree Traversal](trees/check-tree-traversal.java)
+- [Random Node of a binary tree](tree-random-node.java)
 
 ## Backtracking
 
diff --git a/algorithms/Java/trees/tree-random-node.java b/algorithms/Java/trees/tree-random-node.java
new file mode 100644
index 00000000..19264835
--- /dev/null
+++ b/algorithms/Java/trees/tree-random-node.java
@@ -0,0 +1,109 @@
+/** 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;
+    }
+}
+
+class Tree {
+
+    // Using a arraylist to store the inorder traversal of the given binary tree
+    static ArrayList<Integer> list = new ArrayList<Integer>();
+    // root of Tree
+    Node root;
+
+    Tree() {
+        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);
+
+    }
+
+
+    public static void main(String[] args) {
+        Tree tree = new Tree();
+
+
+        tree.root = new Node(1);
+        tree.root.left = new Node(12);
+        tree.root.right = new Node(9);
+        tree.root.left.left = new Node(5);
+        tree.root.left.right = new Node(6);
+
+        tree.getrandom(tree.root);
+
+
+    }
+}
+
+
+/** 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)
+ */
+