Check Bitonicity of an Array in C++

Given an array arr[N] of N integers, the task is to check whether the given array is bitonic or not. If the given array is bitonic then print “Yes its a bitonic array”, else print “No its not a bitonic array”.

A Bitonic array is when the array is in strictly increasing order first and then in strictly decreasing order.

Like this array arr[] = {1, 2, 3, 4, 2, -1, -5} is a bitonic array, because till 4 it is in strictly increasing order and after 4 it is in strictly decreasing order.

Input 

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

Output 

Yes its a bitonic array

Explanation 

1< 3 < 5 > 4 > 2 >0, so yes it is a bitonic array.

Input 

arr[] = {1, 2, 3, 4, 5, 0, -1, -2, 6, -4}

Output 

No its not a bitonic array

Approach used below is as follows to solve the problem

• Iterate every element of an array and check that the previous element is smaller than the current element.

• When the previous element is not smaller than the current element break.

• Check if the previous element is larger than the current, else return false and exit.

• If reached the end of an array return true.

Algorithm

Start
Step 1→ Declare array to check for bitonicity of an array
   int check(int arr[], int size)
      declare int i, j
      Loop For i = 1 and i <size and i++
         IF (arr[i] > arr[i - 1])
            Continue
         End
         IF (arr[i] <= arr[i - 1])
            break
         End
         IF(i == size - 1)
            return 1
         End
         Loop For (j = i + 1 and j < size and j++
            IF (arr[j] < arr[j - 1])
               Continue
            End
            IF (arr[j] <= arr[j - 1])
               break
            End
         End
         Set i = j
         IF (i != size)
            return 0
         End
         return 1
Step 2→ In main()
   Declare int arr[] = { -3, 9, 11, 20, 17, 5, 1 }
   Declare int size = sizeof(arr) / sizeof(arr[0])
   Do (check(arr, size) == 1) ? cout << "Yes its a bitonic array" : cout << "no its not a bitonic array"
Stop

Example

 Live Demo

#include <bits/stdc++.h>
using namespace std;
//function to check bitonic or not
int check(int arr[], int size){
   int i, j;
   for (i = 1; i < size; i++){
      if (arr[i] > arr[i - 1])
         continue;
      if (arr[i] <= arr[i - 1])
         break;
   }
   if (i == size - 1)
      return 1;
   for (j = i + 1; j < size; j++){
      if (arr[j] < arr[j - 1])
         continue;
      if (arr[j] >= arr[j - 1])
         break;
   }
   i = j;
   if (i != size)
      return 0;
   return 1;
}
int main(){
   int arr[] = { -3, 9, 11, 20, 17, 5, 1 };
   int size = sizeof(arr) / sizeof(arr[0]);
   (check(arr, size) == 1) ? cout << "Yes its a bitonic array" : cout << "no its not a bitonic array";
   return 0;
}

Output

If run the above code it will generate the following output −

Yes its a bitonic array