Excel Sheet Column Title
<p>Given an integer <code>columnNumber</code>, return <em>its corresponding column title as it appears in an Excel sheet</em>.</p>

<p>For example:</p>

<pre>
A -&gt; 1
B -&gt; 2
C -&gt; 3
...
Z -&gt; 26
AA -&gt; 27
AB -&gt; 28 
...
</pre>

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

<pre>
<strong>Input:</strong> columnNumber = 1
<strong>Output:</strong> &quot;A&quot;
</pre>

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

<pre>
<strong>Input:</strong> columnNumber = 28
<strong>Output:</strong> &quot;AB&quot;
</pre>

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

<pre>
<strong>Input:</strong> columnNumber = 701
<strong>Output:</strong> &quot;ZY&quot;
</pre>

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

<ul>
	<li><code>1 &lt;= columnNumber &lt;= 2<sup>31</sup> - 1</code></li>
</ul>
Math; String
impl Solution {
    #[allow(dead_code)]
    pub fn convert_to_title(column_number: i32) -> String {
        let mut ret = String::from("");
        let mut column_number = column_number;

        while column_number > 0 {
            if column_number <= 26 {
                ret.push((('A' as u8) + (column_number as u8) - 1) as char);
                break;
            } else {
                let mut left = column_number % 26;
                left = if left == 0 { 26 } else { left };
                ret.push((('A' as u8) + (left as u8) - 1) as char);
                column_number = (column_number - 1) / 26;
            }
        }

        ret.chars().rev().collect()
    }
}
