题目
Given a positive integer n, find the smallest integer which has exactly the same digits existing in the integer n and is greater in value than n. If no such positive integer exists, return -1.
Note that the returned integer should fit in 32-bit integer, if there is a valid answer but it does not fit in 32-bit integer, return -1.
解题思路
从后向前找到第一个升序的位置（如果不存在，返回-1），将这个数与从后向前第一个比它大的数进行交换，再把后面的数从小到大排序
代码
class Solution:
def nextGreaterElement(self, n: int) -> int:
s = list(str(n))
l = len(s)
i = l - 2
while i >= 0:
if s[i] < s[i + 1]:
break
i -= 1
if i < 0:
return -1
for j in range(l - 1, i, -1):
if s[j] > s[i]:
s[i], s[j] = s[j], s[i]
break
s[i + 1:] = s[i + 1:][::-1]
res = ''.join(s)
return res if int(res) <= 0x7fffffff else -1
