C++ Program to Modify given array to a non-decreasing array by rotation
Last Updated :
27 Jan, 2022
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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++ 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);
}
Output
YES
Time Complexity: O(N2)
Auxiliary Space: O(N)
