Monotone Increasing Digits
<p>An integer has <strong>monotone increasing digits</strong> if and only if each pair of adjacent digits <code>x</code> and <code>y</code> satisfy <code>x &lt;= y</code>.</p>

<p>Given an integer <code>n</code>, return <em>the largest number that is less than or equal to </em><code>n</code><em> with <strong>monotone increasing digits</strong></em>.</p>

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

<pre>
<strong>Input:</strong> n = 10
<strong>Output:</strong> 9
</pre>

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

<pre>
<strong>Input:</strong> n = 1234
<strong>Output:</strong> 1234
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> n = 332
<strong>Output:</strong> 299
</pre>

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

<ul>
	<li><code>0 &lt;= n &lt;= 10<sup>9</sup></code></li>
</ul>
Greedy; Math
class Solution {
public:
    int monotoneIncreasingDigits(int n) {
        string s = to_string(n);
        int i = 1;
        for (; i < s.size() && s[i - 1] <= s[i]; ++i)
            ;
        if (i < s.size()) {
            for (; i > 0 && s[i - 1] > s[i]; --i) {
                --s[i - 1];
            }
            ++i;
            for (; i < s.size(); ++i) {
                s[i] = '9';
            }
        }
        return stoi(s);
    }
};