C++ Program to Modify given array to a non-decreasing array by rotation

Given an array arr[] of size N (consisting of duplicates), the task is to check if the given array can be converted to a non-decreasing array by rotating it. If it’s not possible to do so, then print “No“. Otherwise, print “Yes“.

Examples:

Input: arr[] = {3, 4, 5, 1, 2}
Output: Yes
Explanation: After 2 right rotations, the array arr[] modifies to {1, 2, 3, 4, 5}

Input: arr[] = {1, 2, 4, 3}
Output: No

Approach: The idea is based on the fact that a maximum of N distinct arrays can be obtained by rotating the given array and check for each individual rotated array, whether it is non-decreasing or not. Follow the steps below to solve the problem:

Initialize a vector, say v, and copy all the elements of the original array into it.
Sort the vector v.
Traverse the original array and perform the following steps:
- Rotate by 1 in each iteration.
- If the array becomes equal to vector v, print “Yes“. Otherwise, print “No“.

Below is the implementation of the above approach:

C++

// C++ program for the above approach 

#include <bits/stdc++.h> 

using namespace std; 

// Function to check if a 
// non-decreasing array can be obtained 
// by rotating the original array 

void rotateArray(vector<int>& arr, int N) 
{ 

    // Stores copy of original array 

    vector<int> v = arr; 

    // Sort the given vector 

    sort(v.begin(), v.end()); 

    // Traverse the array 

    for (int i = 1; i <= N; ++i) { 

        // Rotate the array by 1 

        rotate(arr.begin(), 

               arr.begin() + 1, arr.end()); 

        // If array is sorted 

        if (arr == v) { 

            cout << "YES" << endl; 

            return; 

        } 

    } 

    // If it is not possible to 

    // sort the array 

    cout << "NO" << endl; 
} 

// Driver Code 

int main() 
{ 

    // Given array 

    vector<int> arr = { 3, 4, 5, 1, 2 }; 

    // Size of the array 

    int N = arr.size(); 

    // Function call to check if it is possible 

    // to make array non-decreasing by rotating 

    rotateArray(arr, N); 
}