Program to check if an array is bitonic or not

Given an array of N elements. The task is to check if the array is bitonic or not.
An array is said to be bitonic if the elements in the array are first strictly increasing and then strictly decreasing.

Examples: 

Input: arr[] = {-3, 9, 11, 20, 17, 5, 1}
Output: YES

Input: arr[] = {5, 6, 7, 8, 9, 10, 1, 2, 11};
Output: NO

Approach:

• Start traversing the array and keep checking if the next element is greater than the current element or not.
• If at any point, the next element is not greater than the current element, break the loop.
• Again start traversing from the current element and check if the next element is less than current element or not.
• If at any point before the end of array is reached, if the next element is not less than the current element, break the loop and print NO.
• If the end of array is reached successfully, print YES.

Below is the implementation of above approach: 

C++

// C++ program to check if an array is bitonic
#include <bits/stdc++.h>
using namespace std;

// Function to check if the given array is bitonic
int checkBitonic(int arr[], int n)
{
    int i, j;

    // Check for increasing sequence
    for (i = 1; i < n; i++) {
        if (arr[i] > arr[i - 1])
            continue;

        if (arr[i] <= arr[i - 1])
            break;
    }

    if (i == n - 1)
        return 1;

    // Check for decreasing sequence
    for (j = i + 1; j < n; j++) {
        if (arr[j] < arr[j - 1])
            continue;

        if (arr[j] >= arr[j - 1])
            break;
    }

    i = j;

    if (i != n)
        return 0;

    return 1;
}

// Driver code
int main()
{
    int arr[] = { 1,2,3 };

    int n = sizeof(arr) / sizeof(arr[0]);

    (checkBitonic(arr, n) == 1) ? cout << "YES"
                                : cout << "NO";

    return 0;
}

Java

// Java program to check
// if an array is bitonic
class GFG
{
// Function to check if the
// given array is bitonic
static int checkBitonic(int arr[], int n)
{
    int i, j;

    // Check for increasing sequence
    for (i = 1; i < n; i++)
    {
        if (arr[i] > arr[i - 1])
            continue;

        if (arr[i] <= arr[i - 1])
            break;
    }

    if (i == n - 1)
        return 1;

    // Check for decreasing sequence
    for (j = i + 1; j < n; j++)
    {
        if (arr[j] < arr[j - 1])
            continue;

        if (arr[j] >= arr[j - 1])
            break;
    }

    i = j;

    if (i != n)
        return 0;

    return 1;
}

// Driver Code
public static void main(String args[])
{
    int arr[] = { -3, 9, 7, 20, 17, 5, 1 };

    int n = arr.length;

    System.out.println((checkBitonic(arr, n) == 1) ?
                                             "YES" : "NO");
}
}

// This code is contributed by Bilal

Python3

# Python3 program to check if
# an array is bitonic or not.

# Function to check if the
# given array is bitonic
def checkBitonic(arr, n) :

    # Check for increasing sequence
    for i in range(1, n) :
        if arr[i] > arr[i - 1] :
            continue
        else :
            break

    if i == n-1 :
        return 1

    # Check for decreasing sequence
    for j in range(i + 1, n) :

        if arr[j] < arr[j - 1] :
            continue
        else :
            break

    i = j
    if i != n - 1 :
        return 0

    return 1

# Driver Code
if __name__ == "__main__" :

    arr = [-3, 9, 7, 20, 17, 5, 1]

    n = len(arr)

    if checkBitonic(arr, n) == 1 :
        print("YES")
    else :
        print("NO")

# This code is contributed
# by ANKITRAI1

C#

// C# program to check
// if an array is bitonic
using System;

class GFG
{
// Function to check if the
// given array is bitonic
static int checkBitonic(int []arr,
                        int n)
{
    int i, j;

    // Check for increasing sequence
    for (i = 1; i < n; i++)
    {
        if (arr[i] > arr[i - 1])
            continue;

        if (arr[i] <= arr[i - 1])
            break;
    }

    if (i == n - 1)
        return 1;

    // Check for decreasing sequence
    for (j = i + 1; j < n; j++)
    {
        if (arr[j] < arr[j - 1])
            continue;

        if (arr[j] >= arr[j - 1])
            break;
    }

    i = j;

    if (i != n)
        return 0;

    return 1;
}

// Driver Code
public static void Main()
{
    int []arr = { -3, 9, 7, 20, 17, 5, 1 };

    int n = arr.Length;

    Console.WriteLine((
            checkBitonic(arr, n) == 1) ?
                                 "YES" : "NO");
}
}

// This code is contributed by Bilal

PHP

<?php
// PHP program to check if
// an array is bitonic

// Function to check if the
// given array is bitonic
function checkBitonic(&$arr, $n)
{

    // Check for increasing sequence
    for ($i = 1; $i < $n; $i++)
    {
        if ($arr[$i] > $arr[$i - 1])
            continue;

        if ($arr[$i] <= $arr[$i - 1])
            break;
    }

    if ($i == $n - 1)
        return 1;

    // Check for decreasing sequence
    for ($j = $i + 1; $j < $n; $j++)
    {
        if ($arr[$j] < $arr[$j - 1])
            continue;

        if ($arr[$j] >= $arr[$j - 1])
            break;
    }

    $i = $j;

    if ($i != $n)
        return 0;

    return 1;
}

// Driver code
$arr = array( -3, 9, 7, 20, 17, 5, 1 );

$n = sizeof($arr);

checkBitonic($arr, $n) == 1 ?
               print("YES") : print("NO");

// This code is contributed by ChitraNayal
?>

Javascript

<script>


// Java Script program to check
// if an array is bitonic

// Function to check if the
// given array is bitonic
function checkBitonic(arr,n)
{
    let i, j;

    // Check for increasing sequence
    for (i = 1; i < n; i++)
    {
        if (arr[i] > arr[i - 1])
            continue;

        if (arr[i] <= arr[i - 1])
            break;
    }

    if (i == n - 1)
        return 1;

    // Check for decreasing sequence
    for (j = i + 1; j < n; j++)
    {
        if (arr[j] < arr[j - 1])
            continue;

        if (arr[j] >= arr[j - 1])
            break;
    }

    i = j;

    if (i != n)
        return 0;

    return 1;
}

// Driver Code

    let arr = [ -3, 9, 7, 20, 17, 5, 1 ];

    let n = arr.length;

    document.write((checkBitonic(arr, n) == 1) ?
                                            "YES" : "NO");

// This code is contributed by sravan kumar
</script>

Output

YES

Time Complexity: O(n), As we are traversing the array only once.
Auxiliary Space: O(1), As constant extra space is used.