# Javascript Program to Count rotations required to sort given array in non-increasing order

• Last Updated : 27 Jan, 2022

Given an array arr[] consisting of N integers, the task is to sort the array in non-increasing order by minimum number of anti-clockwise rotations. If it is not possible to sort the array, then print “-1”. Otherwise, print the count of rotations.

Examples:

Input: arr[] = {2, 1, 5, 4, 3}
Output: 2
Explanation: Two anti-clockwise rotations are required to sort the array in decreasing order, i.e. {5, 4, 3, 2, 1}

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

Approach: The idea is to traverse the given array arr[] and count the number of indices satisfying arr[i + 1] > arr[i]. Follow the steps below to solve the problem:

• Store the count of arr[i + 1] > arr[i] in a variable and also store the index when arr[i+1] > arr[i].
• If the value of count is N – 1, then the array is sorted in non-decreasing order. The required steps are exactly (N – 1).
• If the value of count is 0, then the array is already sorted in non-increasing order.
• If the value of count is 1 and arr[0] ≤ arr[N – 1], then the required number of rotations is equal to (index + 1), by performing shifting of all the numbers upto that index. Also, check if arr[0] ≤ arr[N – 1] to ensure if the sequence is non-increasing.
• Otherwise, it is not possible to sort the array in non-increasing order.

Below is the implementation of the above approach:

## Javascript



Output:

2

Time Complexity: O(N)
Auxiliary Space: O(1)

Please refer complete article on Count rotations required to sort given array in non-increasing order for more details!

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