Maximum Swap
<p>You are given an integer <code>num</code>. You can swap two digits at most once to get the maximum valued number.</p>

<p>Return <em>the maximum valued number you can get</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> num = 2736
<strong>Output:</strong> 7236
<strong>Explanation:</strong> Swap the number 2 and the number 7.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> num = 9973
<strong>Output:</strong> 9973
<strong>Explanation:</strong> No swap.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>0 &lt;= num &lt;= 10<sup>8</sup></code></li>
</ul>
Greedy; Math
class Solution:
    def maximumSwap(self, num: int) -> int:
        s = list(str(num))
        n = len(s)
        d = list(range(n))
        for i in range(n - 2, -1, -1):
            if s[i] <= s[d[i + 1]]:
                d[i] = d[i + 1]
        for i, j in enumerate(d):
            if s[i] < s[j]:
                s[i], s[j] = s[j], s[i]
                break
        return int(''.join(s))
