Minimum Operations to Sort a String — Python

# Time:  O(n)
# Space: O(1)

# greedy
class Solution(object):
    def minOperations(self, s):
        """
        :type s: str
        :rtype: int
        """
        if all(s[i] <= s[i+1] for i in xrange(len(s)-1)):
            return 0
        if len(s) == 2:
            return -1
        mn = min(s[i] for i in xrange(1, len(s)-1))
        mx = max(s[i] for i in xrange(1, len(s)-1))
        return 1 if s[0] == min(s) or s[-1] == max(s) else 2 if s[-1] >= mn or s[0] <= mx else 3