new_contents: # Time:  O(logn) = O(1)
  # Space: O(logn) = O(1)
  
  class Solution(object):
      def monotoneIncreasingDigits(self, N):
          """
          :type N: int
          :rtype: int
          """
          nums = map(int, list(str(N)))
          leftmost_inverted_idx = len(nums)
          for i in reversed(xrange(1, len(nums))):
              if nums[i-1] > nums[i]:
                  leftmost_inverted_idx = i
                  nums[i-1] -= 1
          for i in xrange(leftmost_inverted_idx, len(nums)):
              nums[i] = 9
          return int("".join(map(str, nums)))
  
subject: Create monotone-increasing-digits.py