Javascript Program to Check if it is possible to sort the array after rotating it

Last Updated : 26 May, 2022

Given an array of size N, the task is to determine whether its possible to sort the array or not by just one shuffle. In one shuffle, we can shift some contiguous elements from the end of the array and place it in the front of the array.
For eg:

A = {2, 3, 1, 2}, we can shift {1, 2} from the end of the array to the front of the array to sort it.
A = {1, 2, 3, 2} since we cannot sort it in one shuffle hence it's not possible to sort the array.

Examples:

Input: arr[] = {1, 2, 3, 4} 
Output: Possible 
Since this array is already sorted hence no need for shuffle.

Input: arr[] = {6, 8, 1, 2, 5}
Output: Possible
Place last three elements at the front 
in the same order i.e. {1, 2, 5, 6, 8}

Approach:

Check if the array is already sorted or not. If yes return true.
Else start traversing the array elements until the current element is smaller than next element. Store that index where arr[i] > arr[i+1].
Traverse from that point and check if from that index elements are in increasing order or not.
If above both conditions satisfied then check if last element is smaller than or equal to the first element of given array.
Print "Possible" if above three conditions satisfied else print "Not possible" if any of the above 3 conditions failed.

Below is the implementation of above approach:

JavaScript

<script>
// Javascript implementation of above approach  
// check if array is sorted 
    function is_sorted(a)
    {
        let c1=0,c2=0;
        // if array is ascending 
        for(let i=0;i<n-1;i++)
        {
            if(a[i]<=a[i+1])
            {
                c1++;
            }
        }
        // if array is descending 
        for(let i=1;i<n;i++) 
        { 
            if(a[i]<=a[i-1]) 
                c2++; 
        } 
        if(c1==n||c2==n)
        {
            return true;
        }
        return false;
    }
    // Function to check if it is possible
    function isPossible(a,n)
    {
        // step 1
        if (is_sorted(a,n))
        {
            document.write("Possible");    
        }
        else
        {
            // break where a[i] > a[i+1] 
            let flag = true;
            let i;
            for (i = 0; i < n - 1; i++)
            {
                if (a[i] > a[i + 1])
                {
                    break;
                }
            }
            // break point + 1  
            i++;
            // check whether the sequence is  
            // further increasing or not  
            for (let k = i; k < n - 1; k++)
            {
                if (a[k] > a[k + 1])
                {
                    flag = false;  
                    break;
                }
            }
            // If not increasing after break point  
            if (!flag)  
            {
                return false; 
            }
            else
            {
                // last element <= First element  
                if (a[n - 1] <= a[0])  
                    return true;  
    
                else
                    return false;  
            }
        }
            
        return false; 
    }
    // Driver code  
    let arr=[3, 1, 2, 2, 3];
    let n = arr.length;
    if(isPossible(arr, n))
        document.write("Possible");
    else
        document.write("Not Possible");
        
    // This code is contributed by avanitrachhadiya2155
</script>