Monotone Increasing Digits

Monotone Increasing Digits.py

class Solution:
    def monotoneIncreasingDigits(self, N: int) -> int:
        n=N
        if n==10:
            return 9
        if n<10:
            return n
        arr=[int(i) for i in str(n)]
        for i in range (len(arr)-1):
            if arr[i]>arr[i+1]:
                while i>0 and arr[i]<=arr[i-1]:
                    i-=1
                arr[i]-=1
                for j in range (i+1,len(arr)):
                    arr[j]=9
                res=int(''.join([str(k) for k in arr]))
                return res
        return n