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C++ Program for Check if an array is sorted and rotated

  • Last Updated : 24 Jan, 2022

Given an array of N distinct integers. The task is to write a program to check if this array is sorted and rotated counter-clockwise. A sorted array is not considered as sorted and rotated, i.e., there should at least one rotation.
Examples
 

Input : arr[] = { 3, 4, 5, 1, 2 }
Output : YES
The above array is sorted and rotated.
Sorted array: {1, 2, 3, 4, 5}. 
Rotating this sorted array clockwise 
by 3 positions, we get: { 3, 4, 5, 1, 2}

Input: arr[] = {7, 9, 11, 12, 5}
Output: YES

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

Input: arr[] = {3, 4, 6, 1, 2, 5}
Output: NO

Approach
 

  • Find the minimum element in the array.
  • Now, if the array is sorted and then rotate all the elements before the minimum element will be in increasing order and all elements after the minimum element will also be in increasing order.
  • Check if all elements before minimum element are in increasing order.
  • Check if all elements after minimum element are in increasing order.
  • Check if the last element of the array is smaller than the starting element.
  • If all of the above three conditions satisfies then print YES otherwise print NO.

Below is the implementation of the above idea: 
 

C++




// CPP program to check if an array is
// sorted and rotated clockwise
#include <climits>
#include <iostream>
  
using namespace std;
  
// Function to check if an array is
// sorted and rotated clockwise
void checkIfSortRotated(int arr[], int n)
{
    int minEle = INT_MAX;
    int maxEle = INT_MIN;
  
    int minIndex = -1;
  
    // Find the minimum element
    // and it's index
    for (int i = 0; i < n; i++) {
        if (arr[i] < minEle) {
            minEle = arr[i];
            minIndex = i;
        }
    }
  
    int flag1 = 1;
  
    // Check if all elements before minIndex
    // are in increasing order
    for (int i = 1; i < minIndex; i++) {
        if (arr[i] < arr[i - 1]) {
            flag1 = 0;
            break;
        }
    }
  
    int flag2 = 1;
  
    // Check if all elements after minIndex
    // are in increasing order
    for (int i = minIndex + 1; i < n; i++) {
        if (arr[i] < arr[i - 1]) {
            flag2 = 0;
            break;
        }
    }
  
    // Check if last element of the array
    // is smaller than the element just
    // starting element of the array
    // for arrays like [3,4,6,1,2,5] - not circular array
    if (flag1 && flag2 && (arr[n - 1] < arr[0]))
        cout << "YES";
    else
        cout << "NO";
}
  
// Driver code
int main()
{
    int arr[] = { 3, 4, 5, 1, 2 };
    int n = sizeof(arr) / sizeof(arr[0]);
  
    // Function Call
    checkIfSortRotated(arr, n);
    return 0;
}
Output
YES

Please refer complete article on Check if an array is sorted and rotated for more details!


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