Next Greater Element III
<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>
Math; Two Pointers; String
class Solution:
    def nextGreaterElement(self, n: int) -> int:
        cs = list(str(n))
        n = len(cs)
        i, j = n - 2, n - 1
        while i >= 0 and cs[i] >= cs[i + 1]:
            i -= 1
        if i < 0:
            return -1
        while cs[i] >= cs[j]:
            j -= 1
        cs[i], cs[j] = cs[j], cs[i]
        cs[i + 1 :] = cs[i + 1 :][::-1]
        ans = int(''.join(cs))
        return -1 if ans > 2**31 - 1 else ans
