Program to check whether an 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 −

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