Maximum Difference by Remapping a Digit
<p>You are given an integer <code>num</code>. You know that Bob will sneakily <strong>remap</strong> one of the <code>10</code> possible digits (<code>0</code> to <code>9</code>) to another digit.</p>

<p>Return <em>the difference between the maximum and minimum&nbsp;values Bob can make by remapping&nbsp;<strong>exactly</strong> <strong>one</strong> digit in </em><code>num</code>.</p>

<p><strong>Notes:</strong></p>

<ul>
	<li>When Bob remaps a digit <font face="monospace">d1</font>&nbsp;to another digit <font face="monospace">d2</font>, Bob replaces all occurrences of <code>d1</code>&nbsp;in <code>num</code>&nbsp;with <code>d2</code>.</li>
	<li>Bob can remap a digit to itself, in which case <code>num</code>&nbsp;does not change.</li>
	<li>Bob can remap different digits for obtaining minimum and maximum values respectively.</li>
	<li>The resulting number after remapping can contain leading zeroes.</li>
</ul>

<p>&nbsp;</p>
<p><strong>Example 1:</strong></p>

<pre>
<strong>Input:</strong> num = 11891
<strong>Output:</strong> 99009
<strong>Explanation:</strong> 
To achieve the maximum value, Bob can remap the digit 1 to the digit 9 to yield 99899.
To achieve the minimum value, Bob can remap the digit 1 to the digit 0, yielding 890.
The difference between these two numbers is 99009.
</pre>

<p><strong>Example 2:</strong></p>

<pre>
<strong>Input:</strong> num = 90
<strong>Output:</strong> 99
<strong>Explanation:</strong>
The maximum value that can be returned by the function is 99 (if 0 is replaced by 9) and the minimum value that can be returned by the function is 0 (if 9 is replaced by 0).
Thus, we return 99.</pre>

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

<ul>
	<li><code>1 &lt;= num &lt;= 10<sup>8</sup></code></li>
</ul>
Greedy; Math
class Solution {
    public int minMaxDifference(int num) {
        String s = String.valueOf(num);
        int mi = Integer.parseInt(s.replace(s.charAt(0), '0'));
        for (char c : s.toCharArray()) {
            if (c != '9') {
                return Integer.parseInt(s.replace(c, '9')) - mi;
            }
        }
        return num - mi;
    }
}