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Check if an array represents Inorder of Binary Search tree or not
• Difficulty Level : Easy
• Last Updated : 14 Jan, 2019

Given an array of N element. The task is to check if it is Inorder traversal of any Binary Search Tree or not. Print “Yes” if it is Inorder traversal of any Binary Search Tree else print “No”.

Examples:

```Input : arr[] = { 19, 23, 25, 30, 45 }
Output : Yes

Input : arr[] = { 19, 23, 30, 25, 45 }
Output : No
```

Recommended: Please solve it on “PRACTICE” first, before moving on to the solution.

The idea is to use the fact that the inorder traversal of Binary Search Tree is sorted. So, just check if given array is sorted or not.

C++

 `// C++ program to check if a given array is sorted``// or not.``#include``using` `namespace` `std;`` ` `// Function that returns true if array is Inorder``// traversal of any Binary Search Tree or not.``bool` `isInorder(``int` `arr[], ``int` `n)``{``    ``// Array has one or no element``    ``if` `(n == 0 || n == 1)``        ``return` `true``;`` ` `    ``for` `(``int` `i = 1; i < n; i++)`` ` `        ``// Unsorted pair found``        ``if` `(arr[i-1] > arr[i])``            ``return` `false``;`` ` `    ``// No unsorted pair found``    ``return` `true``;``}`` ` `// Driver code``int` `main()``{``    ``int` `arr[] = { 19, 23, 25, 30, 45 };``    ``int` `n = ``sizeof``(arr)/``sizeof``(arr[0]);``     ` `    ``if` `(isInorder(arr, n))``        ``cout << ``"Yesn"``;``    ``else``        ``cout << ``"Non"``;``         ` `  ``return` `0;``}`

Java

 `// Java program to check if a given array is sorted ``// or not. `` ` `class` `GFG {`` ` `// Function that returns true if array is Inorder ``// traversal of any Binary Search Tree or not. ``    ``static` `boolean` `isInorder(``int``[] arr, ``int` `n) {``        ``// Array has one or no element ``        ``if` `(n == ``0` `|| n == ``1``) {``            ``return` `true``;``        ``}`` ` `        ``for` `(``int` `i = ``1``; i < n; i++) ``// Unsorted pair found ``        ``{``            ``if` `(arr[i - ``1``] > arr[i]) {``                ``return` `false``;``            ``}``        ``}`` ` `        ``// No unsorted pair found ``        ``return` `true``;``    ``}``// Drivers code `` ` `    ``public` `static` `void` `main(String[] args) {``        ``int` `arr[] = {``19``, ``23``, ``25``, ``30``, ``45``};``        ``int` `n = arr.length;``        ``if` `(isInorder(arr, n)) {``            ``System.out.println(``"Yes"``);``        ``} ``else` `{``            ``System.out.println(``"Non"``);``        ``}``    ``}``}``//This code is contributed by 29AjayKumar `

Python3

 `# Python 3 program to check if a given array ``# is sorted or not.`` ` `# Function that returns true if array is Inorder``# traversal of any Binary Search Tree or not.``def` `isInorder(arr, n):``     ` `    ``# Array has one or no element``    ``if` `(n ``=``=` `0` `or` `n ``=``=` `1``):``        ``return` `True`` ` `    ``for` `i ``in` `range``(``1``, n, ``1``):``         ` `        ``# Unsorted pair found``        ``if` `(arr[i ``-` `1``] > arr[i]):``            ``return` `False`` ` `    ``# No unsorted pair found``    ``return` `True`` ` `# Driver code``if` `__name__ ``=``=` `'__main__'``:``    ``arr ``=` `[``19``, ``23``, ``25``, ``30``, ``45``]``    ``n ``=` `len``(arr)``     ` `    ``if` `(isInorder(arr, n)):``        ``print``(``"Yes"``)``    ``else``:``        ``print``(``"No"``)``         ` `# This code is contributed by``# Sahil_Shelangia`

C#

 `// C# program to check if a given ``// array is sorted or not. ``using` `System;`` ` `class` `GFG``{`` ` `// Function that returns true if ``// array is Inorder traversal of ``// any Binary Search Tree or not. ``static` `bool` `isInorder(``int``[] arr, ``int` `n)``{``    ``// Array has one or no element ``    ``if` `(n == 0 || n == 1) ``    ``{``        ``return` `true``;``    ``}``     ` `    ``// Unsorted pair found ``    ``for` `(``int` `i = 1; i < n; i++) ``    ``{``        ``if` `(arr[i - 1] > arr[i])``        ``{``            ``return` `false``;``        ``}``    ``}`` ` `    ``// No unsorted pair found ``    ``return` `true``;``}`` ` `// Driver code ``public` `static` `void` `Main() ``{``    ``int` `[]arr = {19, 23, 25, 30, 45};``    ``int` `n = arr.Length;``    ``if` `(isInorder(arr, n)) ``    ``{``        ``Console.Write(``"Yes"``);``    ``} ``    ``else``    ``{``        ``Console.Write(``"Non"``);``    ``}``}``}`` ` `// This code is contributed by Rajput-Ji`

PHP

 ` ``\$arr``[``\$i``])``            ``return` `false;`` ` `    ``// No unsorted pair found``    ``return` `true;``}`` ` `// Driver code``\$arr` `= ``array``(19, 23, 25, 30, 45);``\$n` `= sizeof(``\$arr``);`` ` `if` `(isInorder(``\$arr``, ``\$n``))``    ``echo` `"Yes"``;``else``    ``echo` `"No"``;`` ` `// This code is contributed``// by Akanksha Rai``?>`

Output:
```Yes
```

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