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
func convertToTitle(columnNumber int) string {
	res := []rune{}
	for columnNumber != 0 {
		columnNumber -= 1
		res = append([]rune{rune(columnNumber%26 + int('A'))}, res...)
		columnNumber /= 26
	}
	return string(res)
}