LeetCode #556. Next Greater Element III

题目描述：

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

class Solution {
public:
    int nextGreaterElement(int n) {
        string s=to_string(n);
        int i=s.size()-2;
        while(i>=0&&s[i]>=s[i+1]) i--;
        if(i<0) return -1;
        int j=i;
        while(j<s.size()-1&&s[j+1]>s[i]) j++;
        swap(s[i],s[j]);
        reverse(s.begin()+i+1,s.end());
        long long result=stoll(s);
        if(result>INT_MAX) return -1;
        else return result;
    }
};