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

  • Last Updated : 24 Jan, 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: 
 

  1. 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.
  2. 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: 
 

  1. Check if the array is already sorted or not. If yes return true.
  2. Else start traversing the array elements until the current element is smaller than next element. Store that index where arr[i] > arr[i+1].
  3. Traverse from that point and check if from that index elements are in increasing order or not.
  4. If above both conditions satisfied then check if last element is smaller than or equal to the first element of given array.
  5. 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: 
 

Java




// Java implementation of above approach 
class solution
{
    //check if array is sorted
static boolean is_sorted(int a[],int n)
{
    int c1=0,c2=0;
    //if array is ascending
    for(int i=0;i<n-1;i++)
    {
        if(a[i]<=a[i+1])
        c1++;
    }
      
    //if array is descending
    for(int 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 
static boolean isPossible(int a[], int n) 
    // step 1 
    if (is_sorted(a,n)) { 
        System.out.println("Possible"); 
    
    
    else
    
        // break where a[i] > a[i+1] 
        boolean flag = true
        int 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 (int 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 
public static void main(String[] args) 
    
    int arr[] = { 3, 1, 2, 2, 3 }; 
    int n = arr.length; 
    
    if (isPossible(arr, n)) 
        System.out.println("Possible"); 
    
    else
        System.out.println("Not Possible"); 
    
}
//contributed by Arnab Kundu
Output: 
Possible

 

Please refer complete article on Check if it is possible to sort the array after rotating it for more details!


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