[LeetCode]Next Greater Element III

题目描述：

LeetCode 556. Next Greater Element III

Given a positive 32-bit integer n, you need to find the smallest 32-bit integer which has exactly the same digits existing in the integer n and is greater in value than n. If no such positive 32-bit integer exists, you need to return -1.

Example 1:

Input: 12Output: 21

Example 2:

Input: 21Output: -1

题目大意：

给定一个32位正整数n，寻找大于n，并且所含数字与n中各位数字相等的最小32位正整数。若不存在，返回-1。

解题思路：

本题目是Next Permutation的变形，参考Next Permutation的解法。

Python代码：

class Solution(object):
    def nextGreaterElement(self, n):
        """
        :type n: int
        :rtype: int
        """
        nums = list(str(n))
        size = len(nums)
        for x in range(size - 1, -1, -1):
            if nums[x - 1] < nums[x]:
                break
        if x > 0:
            for y in range(size - 1, -1, -1):
                if nums[y] > nums[x - 1]:
                    nums[x - 1], nums[y] = nums[y], nums[x - 1]
                    break
        for z in range((size - x) / 2):
            nums[x + z], nums[size - z - 1] = nums[size - z - 1], nums[x + z]
        ans = int(''.join(nums))
        return n < ans <= 0x7FFFFFFF and ans or -1