<p>Given a positive integer <code>n</code>, find <em>the smallest integer which has exactly the same digits existing in the integer</em> <code>n</code> <em>and is greater in value than</em> <code>n</code>. If no such positive integer exists, return <code>-1</code>.</p>

<p><strong>Note</strong> that the returned integer should fit in <strong>32-bit integer</strong>, if there is a valid answer but it does not fit in <strong>32-bit integer</strong>, return <code>-1</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre><strong>Input:</strong> n = 12
<strong>Output:</strong> 21
</pre><p><strong class="example">Example 2:</strong></p>
<pre><strong>Input:</strong> n = 21
<strong>Output:</strong> -1
</pre>
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= n &lt;= 2<sup>31</sup> - 1</code></li>
</ul>

class Solution {
public:
    int nextGreaterElement(int n) {
        if (n < 10) return -1;

        auto num = to_string(n);
        const int size = num.size();

        int i = size - 2;

        for (; i >= 0; --i) {
            if (num[i] < num[i + 1]) {
                break;
            }
        }

        if (i == -1) {
            return -1;
        }

        std::reverse(begin(num) + i + 1, end(num));

        int idx = std::upper_bound(begin(num) + i + 1, end(num), num[i]) - begin(num);

        swap(num[idx], num[i]);

        auto res = stol(num);
        return res <= INT_MAX ? res : -1;
    }
};
7400