Check if Array is Sorted and Rotated in Python

Suppose we have an array called nums, we have to check whether the array was originally sorted in non-decreasing order, and then rotated some number of positions (may be zero) or not. Duplicates may also present in the array.

So, if the input is like nums = [12,15,2,5,6,9], then the output will be True, because it is rotated to the right for two places

To solve this, we will follow these steps −

• j := 0

• while j < size of nums - 1 and nums[j] <= nums[j + 1], do

  • j := j + 1

• res := (subarray of nums from index j + 1 to end of nums) concatenate (subarray of nums from index 0 to j of nums)

• for i in range 0 to size of res - 1, do

  • if res[i] > res[i + 1], then

    • return False

• return True

Example (Python)

Let us see the following implementation to get better understanding −

 Live Demo

def solve(nums):
   j = 0
   while (j < len(nums) - 1 and nums[j] <= nums[j + 1]):
      j += 1
   res = nums[j + 1 : len(nums)] + nums[0:j + 1]
   for i in range(len(res) - 1):
      if res[i] > res[i + 1]:
         return False
   return True

nums = [12,15,2,5,6,9]
print(solve(nums))

Input

[12,15,2,5,6,9]

Output

True