Check if an array represents Inorder of Binary Search tree or not

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

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. 

Implementation:

C++

// C++ program to check if a given array is sorted
// or not.
#include<bits/stdc++.h>
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 << "Yes";
    else
        cout << "No";

  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("No");
        }
    }
}
//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("No");
    }
}
}

// This code is contributed by Rajput-Ji

PHP

<?php
// PHP 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.
function isInorder($arr, $n)
{
    // Array has one or no element
    if ($n == 0 || $n == 1)
        return true;

    for ($i = 1; $i < $n; $i++)

        // Unsorted pair found
        if ($arr[$i - 1] > $arr[$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
?>

Javascript

<script>
// javascript 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.
    function isInorder(arr , n)
    {

        // Array has one or no element
        if (n == 0 || n == 1) {
            return true;
        }

        for (i = 1; i < n; i++) // Unsorted pair found
        {
            if (arr[i - 1] > arr[i]) {
                return false;
            }
        }

        // No unsorted pair found
        return true;
    }

    // Drivers code
        var arr = [ 19, 23, 25, 30, 45 ];
        var n = arr.length;
        if (isInorder(arr, n)) {
            document.write("Yes");
        } else {
            document.write("No");
        }

// This code is contributed by Rajput-Ji
</script>

Output

Yes

Time complexity: O(n) where n is the size of array
Auxiliary Space: O(1)