[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: 12
Output: 21 

Example 2:

Input: 21
Output: -1

思路：

首先，将整型数字转换成字符串，然后利用stl提供的next_permutation()函数，求字符的全排列，对应的字符串再转换回整型，随时记录大小即可。

int nextGreaterElement2(int n) {
        char buf[];
        sprintf(buf, "%d", n);
        string s = buf;
        puts(s.data());
        sort(s.begin(), s.end());
        long long ans = INT_MAX + 1LL;
        do {
            long long tmp = atoll(s.c_str());
            if (tmp > n) {
                ans = min(ans, tmp);
            }
        } while (next_permutation(s.begin(), s.end()));
        return ans <= INT_MAX ? ans : -;
    }