Program to calculate Bitonicity of an Array

Last Updated : 10 May, 2021

Given an array of $N$ integers. The task is to find the Bitonicity of the given array.
The Bitonicity of an array arr[] can be defined as:

B[i] = 0,         if i = 0.
     = B[i-1] + 1, if arr[i] > arr[i-1]
     = B[i-1] - 1, if arr[i] < arr[i-1]
     = B[i-1],     if arr[i] = arr[i-1]    

Bitonicity will be last element of array B[].

Examples:

Input : arr[] = {1, 2, 3, 4, 5}
Output : 4

Input : arr[] = {1, 4, 5, 3, 2}
Output : 0

Given that the Bitonicity of an array arr[] can be defined as:

B[i] = 0,         if i = 0.
     = B[i-1] + 1, if arr[i] > arr[i-1]
     = B[i-1] - 1, if arr[i] < arr[i-1]
     = B[i-1],     if arr[i] = arr[i-1]

Bitonicity will be last element of array B[].

From the above expression, it can be deduced that:

The bitonicity of the array is initially 0.
It increases by 1 on moving to next element if the next element is greater than previous element.
It decreases by 1 on moving to next element if the next element is greater than previous element.

The idea is to take a variable $bt = 0$ and start traversing the array, if the next element is greater than current, increment bt by 1 and if the next element is smaller than current then decrement bt by 1.
Below is the implementation of the above approach:

C++

// C++ program to find bitonicity
// of an array
#include <iostream>
using namespace std;
 
// Function to find the bitonicity
// of an array
int findBitonicity(int arr[], int n)
{
    int bt = 0;
 
    for (int i = 1; i < n; i++) {
        if (arr[i] > arr[i - 1])
            bt++;
        else if (arr[i] < arr[i - 1])
            bt--;
    }
 
    return bt;
}
 
// Driver Code
int main()
{
    int arr[] = { 1, 2, 3, 4, 5, 6, 4, 3 };
 
    int n = sizeof(arr) / sizeof(arr[0]);
 
    cout << "Bitonicity = " << findBitonicity(arr, n);
 
    return 0;
}

Java

// Java program to find bitonicity
// of an array
import java.util.*;
import java.lang.*;
 
class GFG
{
     
// Function to find the bitonicity
// of an array
static int findBitonicity(int[] arr,
                          int n)
{
    int bt = 0;
 
    for (int i = 1; i < n; i++)
    {
        if (arr[i] > arr[i - 1])
            bt++;
        else if (arr[i] < arr[i - 1])
            bt--;
    }
 
    return bt;
}
 
// Driver Code
public static void main(String args[])
{
    int arr[] = { 1, 2, 3, 4, 5, 6, 4, 3 };
 
    int n = arr.length;
 
    System.out.print("Bitonicity = " +
              findBitonicity(arr, n));
}
}
 
// This code is contributed
// by Akanksha Rai

Python3

# Python3 program to find bitonicity
# of an array
 
# Function to find the bitonicity
# of an array
def findBitonicity(arr, n):
    bt = 0
 
    for i in range(1, n, 1):
        if (arr[i] > arr[i - 1]):
            bt += 1
        elif (arr[i] < arr[i - 1]):
            bt -= 1
 
    return bt
 
# Driver Code
if __name__ == '__main__':
    arr = [1, 2, 3, 4, 5, 6, 4, 3]
 
    n = len(arr)
 
    print("Bitonicity =",
           findBitonicity(arr, n))
 
# This code is contributed by
# Surendra_Gangwar

C#

// C# program to find bitonicity
// of an array
using System;
 
class GFG
{
// Function to find the bitonicity
// of an array
static int findBitonicity(int[] arr,
                          int n)
{
    int bt = 0;
 
    for (int i = 1; i < n; i++)
    {
        if (arr[i] > arr[i - 1])
            bt++;
        else if (arr[i] < arr[i - 1])
            bt--;
    }
 
    return bt;
}
 
// Driver Code
public static void Main()
{
    int[] arr = { 1, 2, 3, 4, 5, 6, 4, 3 };
 
    int n = arr.Length;
 
    Console.Write("Bitonicity = " +
                  findBitonicity(arr, n));
}
}
 
// This code is contributed
// by Akanksha Rai

PHP

<?php
// PHP program to find bitonicity
// of an array
 
// Function to find the bitonicity
// of an array
function findBitonicity(&$arr, $n)
{
    $bt = 0;
 
    for ($i = 1; $i < $n; $i++)
    {
        if ($arr[$i] > $arr[$i - 1])
            $bt++;
        else if ($arr[$i] < $arr[$i - 1])
            $bt--;
    }
 
    return $bt;
}
 
// Driver Code
$arr = array(1, 2, 3, 4, 5, 6, 4, 3 );
 
$n = sizeof($arr);
 
echo ("Bitonicity = ");
echo findBitonicity($arr, $n);
 
// This code is contributed
// by Shivi_Aggarwal
?>

Javascript

<script>
 
// Javascript program to find bitonicity
// of an array   
 
// Function to find the bitonicity
// of an array
    function findBitonicity(arr , n)
    {
        var bt = 0;
 
        for (i = 1; i < n; i++) {
            if (arr[i] > arr[i - 1])
                bt++;
            else if (arr[i] < arr[i - 1])
                bt--;
        }
 
        return bt;
    }
 
    // Driver Code
     
        var arr = [ 1, 2, 3, 4, 5, 6, 4, 3 ];
 
        var n = arr.length;
 
        document.write("Bitonicity = " + findBitonicity(arr, n));
 
// This code contributed by gauravrajput1
 
</script>

Output:

Bitonicity = 3

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