<p>You are given an integer <code>num</code>. You will apply the following steps exactly <strong>two</strong> times:</p>

<ul>
	<li>Pick a digit <code>x (0 &lt;= x &lt;= 9)</code>.</li>
	<li>Pick another digit <code>y (0 &lt;= y &lt;= 9)</code>. The digit <code>y</code> can be equal to <code>x</code>.</li>
	<li>Replace all the occurrences of <code>x</code> in the decimal representation of <code>num</code> by <code>y</code>.</li>
	<li>The new integer <strong>cannot</strong> have any leading zeros, also the new integer <strong>cannot</strong> be 0.</li>
</ul>

<p>Let <code>a</code> and <code>b</code> be the results of applying the operations to <code>num</code> the first and second times, respectively.</p>

<p>Return <em>the max difference</em> between <code>a</code> and <code>b</code>.</p>

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

<pre>
<strong>Input:</strong> num = 555
<strong>Output:</strong> 888
<strong>Explanation:</strong> The first time pick x = 5 and y = 9 and store the new integer in a.
The second time pick x = 5 and y = 1 and store the new integer in b.
We have now a = 999 and b = 111 and max difference = 888
</pre>

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

<pre>
<strong>Input:</strong> num = 9
<strong>Output:</strong> 8
<strong>Explanation:</strong> The first time pick x = 9 and y = 9 and store the new integer in a.
The second time pick x = 9 and y = 1 and store the new integer in b.
We have now a = 9 and b = 1 and max difference = 8
</pre>

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

<ul>
	<li><code>1 &lt;= num &lt;= 10<sup>8</sup></code></li>
</ul>

class Solution:
    def maxDiff(self, num: int) -> int:
        small = big = str(num)

        for i, c in enumerate(small):
            if c not in '01':
                small = small.replace(c, '0' if i else '1')
                break

        for c in big:
            if c != '9':
                big = big.replace(c, '9')
                break

        return int(big) - int(small)

16500