# Maximum height of the binary search tree created from the given array

• Last Updated : 30 Jun, 2021

Given an array arr[] of N integers, the task is to make two binary search trees. One while traversing from the left side of the array and another while traversing from the right and find which tree has a greater height.
Examples:

```Input: arr[] = {2, 1, 3, 4}
Output: 0
BST starting from first index           BST starting from last index
2                                             4
/ \                                           /
1   3                                         3
\                                       /
4                                     1
\
2

Input: arr[] = {1, 2, 6, 3, 5}
Output: 1```

Prerequisites: Inserting a node in a Binary Search tree and Finding the height of a binary tree.
Approach:

• Create a binary search tree while inserting the nodes starting from the first element of the array till the last and find the height of this created tree say leftHeight.
• Create another binary search tree while inserting the nodes starting from the last element of the array till the first and find the height of this created tree say rightHeight.
• Print the maximum of these calculated heights i.e. max(leftHeight, rightHeight)

Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach``#include ``using` `namespace` `std;` `struct` `node {``    ``int` `key;``    ``struct` `node *left, *right;``};` `// A utility function to create a new BST node``struct` `node* newNode(``int` `item)``{``    ``struct` `node* temp = (``struct` `node*)``malloc``(``sizeof``(``struct` `node));``    ``temp->key = item;``    ``temp->left = temp->right = NULL;``    ``return` `temp;``}` `/* A utility function to insert a new node with given key in BST */``struct` `node* insert(``struct` `node* node, ``int` `key)``{``    ``/* If the tree is empty, return a new node */``    ``if` `(node == NULL)``        ``return` `newNode(key);` `    ``/* Otherwise, recur down the tree */``    ``if` `(key < node->key)``        ``node->left = insert(node->left, key);``    ``else` `if` `(key > node->key)``        ``node->right = insert(node->right, key);` `    ``/* return the (unchanged) node pointer */``    ``return` `node;``}` `/* Compute the "maxDepth" of a tree -- the number of``    ``nodes along the longest path from the root node``    ``down to the farthest leaf node.*/``int` `maxDepth(node* node)``{``    ``if` `(node == NULL)``        ``return` `0;``    ``else` `{``        ``/* compute the depth of each subtree */``        ``int` `lDepth = maxDepth(node->left);``        ``int` `rDepth = maxDepth(node->right);` `        ``/* use the larger one */``        ``if` `(lDepth > rDepth)``            ``return` `(lDepth + 1);``        ``else``            ``return` `(rDepth + 1);``    ``}``}` `// Function to return the maximum``// heights among the BSTs``int` `maxHeight(``int` `a[], ``int` `n)``{``    ``// Create a BST starting from``    ``// the first element``    ``struct` `node* rootA = NULL;``    ``rootA = insert(rootA, a[0]);``    ``for` `(``int` `i = 1; i < n; i++)``        ``insert(rootA, a[i]);` `    ``// Create another BST starting``    ``// from the last element``    ``struct` `node* rootB = NULL;``    ``rootB = insert(rootB, a[n - 1]);``    ``for` `(``int` `i = n - 2; i >= 0; i--)``        ``insert(rootB, a[i]);` `    ``// Find the heights of both the trees``    ``int` `A = maxDepth(rootA) - 1;``    ``int` `B = maxDepth(rootB) - 1;` `    ``return` `max(A, B);``}` `// Driver code``int` `main()``{``    ``int` `a[] = { 2, 1, 3, 4 };``    ``int` `n = ``sizeof``(a) / ``sizeof``(a[0]);` `    ``cout << maxHeight(a, n);` `    ``return` `0;``}`

## Java

 `// Java implementation of the approach``class` `GFG``{` `static` `class` `node``{``    ``int` `key;``    ``node left, right;``};` `// A utility function to create a new BST node``static` `node newNode(``int` `item)``{``    ``node temp = ``new` `node();``    ``temp.key = item;``    ``temp.left = temp.right = ``null``;``    ``return` `temp;``}` `/* A utility function to insert``a new node with given key in BST */``static` `node insert(node node, ``int` `key)``{``    ``/* If the tree is empty,``    ``return a new node */``    ``if` `(node == ``null``)``        ``return` `newNode(key);` `    ``/* Otherwise, recur down the tree */``    ``if` `(key < node.key)``        ``node.left = insert(node.left, key);``    ``else` `if` `(key > node.key)``        ``node.right = insert(node.right, key);` `    ``/* return the (unchanged) node pointer */``    ``return` `node;``}` `/* Compute the "maxDepth" of a tree --``the number of nodes along the longest path``from the root node down to the farthest leaf node.*/``static` `int` `maxDepth(node node)``{``    ``if` `(node == ``null``)``        ``return` `0``;``    ``else``    ``{``        ` `        ``/* compute the depth of each subtree */``        ``int` `lDepth = maxDepth(node.left);``        ``int` `rDepth = maxDepth(node.right);` `        ``/* use the larger one */``        ``if` `(lDepth > rDepth)``            ``return` `(lDepth + ``1``);``        ``else``            ``return` `(rDepth + ``1``);``    ``}``}` `// Function to return the maximum``// heights among the BSTs``static` `int` `maxHeight(``int` `a[], ``int` `n)``{``    ``// Create a BST starting from``    ``// the first element``    ``node rootA = ``null``;``    ``rootA = insert(rootA, a[``0``]);``    ``for` `(``int` `i = ``1``; i < n; i++)``        ``rootA = insert(rootA, a[i]);` `    ``// Create another BST starting``    ``// from the last element``    ``node rootB = ``null``;``    ``rootB = insert(rootB, a[n - ``1``]);``    ``for` `(``int` `i = n - ``2``; i >= ``0``; i--)``        ``rootB =insert(rootB, a[i]);` `    ``// Find the heights of both the trees``    ``int` `A = maxDepth(rootA) - ``1``;``    ``int` `B = maxDepth(rootB) - ``1``;` `    ``return` `Math.max(A, B);``}` `// Driver code``public` `static` `void` `main(String args[])``{``    ``int` `a[] = { ``2``, ``1``, ``3``, ``4` `};``    ``int` `n = a.length;` `    ``System.out.println(maxHeight(a, n));``}``}` `// This code is contributed by Arnab Kundu`

## Python3

 `# Python implementation of the approach` `class` `Node:``    ``def` `__init__(``self``, key):``        ``self``.key ``=` `key``        ``self``.left ``=` `None``        ``self``.right ``=` `None` `# A utility function to insert``# a new node with given key in BST */``def` `insert(node: Node, key: ``int``) ``-``> Node:` `    ``# If the tree is empty,``    ``# return a new node */``    ``if` `node ``is` `None``:``        ``return` `Node(key)``    ``# Otherwise, recur down the tree``    ``if` `key < node.key:``        ``node.left ``=` `insert(node.left, key)``    ``elif` `key > node.key:``        ``node.right ``=` `insert(node.right, key)` `    ``# return the (unchanged) node pointer``    ``return` `node` `# Compute the "maxDepth" of a tree --``# the number of nodes along the longest path``# from the root node down to the farthest leaf node.*/``def` `maxDepth(node: Node) ``-``> ``int``:``    ``if` `node ``is` `None``:``        ``return` `0``    ``else``:` `        ``# compute the depth of each subtree``        ``lDepth ``=` `maxDepth(node.left)``        ``rDepth ``=` `maxDepth(node.right)` `        ``# use the larger one``        ``if` `lDepth > rDepth:``            ``return` `lDepth ``+` `1``        ``else``:``            ``return` `rDepth ``+` `1` `# Function to return the maximum``# heights among the BSTs``def` `maxHeight(a: ``list``, n: ``int``) ``-``> ``int``:` `    ``# Create a BST starting from``    ``# the first element``    ``rootA ``=` `Node(a[``0``])``    ``for` `i ``in` `range``(``1``, n):``        ``rootA ``=` `insert(rootA, a[i])` `    ``# Create another BST starting``    ``# from the last element``    ``rootB ``=` `Node(a[n ``-` `1``])``    ``for` `i ``in` `range``(n ``-` `2``, ``-``1``, ``-``1``):``        ``rootB ``=` `insert(rootB, a[i])` `    ``# Find the heights of both the trees``    ``A ``=` `maxDepth(rootA) ``-` `1``    ``B ``=` `maxDepth(rootB) ``-` `1` `    ``return` `max``(A, B)` `# Driver Code``if` `__name__ ``=``=` `"__main__"``:``    ``a ``=` `[``2``, ``1``, ``3``, ``4``]``    ``n ``=` `len``(a)` `    ``print``(maxHeight(a, n))` `# This code is contributed by``# sanjeev2552`

## C#

 `// C# implementation of the approach``using` `System;` `class` `GFG``{``    ``public` `class` `node``    ``{``        ``public` `int` `key;``        ``public` `node left, right;``    ``};``    ` `    ``// A utility function to create a new BST node``    ``static` `node newNode(``int` `item)``    ``{``        ``node temp = ``new` `node();``        ``temp.key = item;``        ``temp.left = temp.right = ``null``;``        ``return` `temp;``    ``}``    ` `    ``/* A utility function to insert``    ``a new node with given key in BST */``    ``static` `node insert(node node, ``int` `key)``    ``{``        ``/* If the tree is empty,``        ``return a new node */``        ``if` `(node == ``null``)``            ``return` `newNode(key);``    ` `        ``/* Otherwise, recur down the tree */``        ``if` `(key < node.key)``            ``node.left = insert(node.left, key);``        ``else` `if` `(key > node.key)``            ``node.right = insert(node.right, key);``    ` `        ``/* return the (unchanged) node pointer */``        ``return` `node;``    ``}``    ` `    ``/* Compute the "maxDepth" of a tree --``    ``the number of nodes along the longest path``    ``from the root node down to the farthest leaf node.*/``    ``static` `int` `maxDepth(node node)``    ``{``        ``if` `(node == ``null``)``            ``return` `0;``        ``else``        ``{``            ` `            ``/* compute the depth of each subtree */``            ``int` `lDepth = maxDepth(node.left);``            ``int` `rDepth = maxDepth(node.right);``    ` `            ``/* use the larger one */``            ``if` `(lDepth > rDepth)``                ``return` `(lDepth + 1);``            ``else``                ``return` `(rDepth + 1);``        ``}``    ``}``    ` `    ``// Function to return the maximum``    ``// heights among the BSTs``    ``static` `int` `maxHeight(``int` `[]a, ``int` `n)``    ``{``        ``// Create a BST starting from``        ``// the first element``        ``node rootA = ``null``;``        ``rootA = insert(rootA, a[0]);``        ``for` `(``int` `i = 1; i < n; i++)``            ``rootA = insert(rootA, a[i]);``    ` `        ``// Create another BST starting``        ``// from the last element``        ``node rootB = ``null``;``        ``rootB = insert(rootB, a[n - 1]);``        ``for` `(``int` `i = n - 2; i >= 0; i--)``            ``rootB =insert(rootB, a[i]);``    ` `        ``// Find the heights of both the trees``        ``int` `A = maxDepth(rootA) - 1;``        ``int` `B = maxDepth(rootB) - 1;``    ` `        ``return` `Math.Max(A, B);``    ``}``    ` `    ``// Driver code``    ``public` `static` `void` `Main()``    ``{``        ``int` `[]a = { 2, 1, 3, 4 };``        ``int` `n = a.Length;``    ` `        ``Console.WriteLine(maxHeight(a, n));``    ``}``}` `// This code is contributed by AnkitRai01`

## Javascript

 ``

Output:

`3`

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