algorithm notes: leetcode#665 non

class :
    def checkPossibility(self, nums):
        """
        :type nums: List[int]
        :rtype: bool
        """
        pos = None
        for i in range(len(nums)-1):
            if nums[i] > nums[i+1]:
                if pos is not None:
                    return False
                pos = i
        return (pos is None or pos==0 or pos==len(nums)-2 or nums[pos-1]<=nums[pos+1] or nums[pos]<=nums[pos+2])